Testing the Undertint App While Painting a Strawberry Daifuku
How I Found Out About Undertint
After posting a video where I was testing a different app, I got an email from a developer named Justin. He told me he built an app called Undertint specifically for his wife, a watercolor artist who was struggling with color mixing formulas and ratios. If you've ever stared at a reference photo wondering how on earth to mix that particular pink, you know exactly the problem he was solving.
I agreed to test the beta, went to the website, and was immediately tickled — the site itself just had this lovely, charming quality to it. The app has since launched and is now available in the App Store, so you can go grab it for yourself.
What Undertint Actually Does
When you open Undertint, you can start by setting up your palette. It comes preloaded with common starter sets — there's a Winsor & Newton palette and a Holbein palette — or you can build your own from scratch. I went with Winsor & Newton since it's close to what I have, even though I've swapped a few colors out over the years.
From there, you click New Study, pull in a photo from your camera roll, and the app gets to work. It simplifies the image and lets you adjust how many colors you want to work with (I went with fewer — I'm a simple person that way). You can also switch to a grayscale Values view, which is great for focusing on light and dark before you think about color at all.
Here's the part I found genuinely impressive: when you tap on any color in your photo, Undertint doesn't just tell you which paint to use. It tells you:
Which two or more paints to mix together
The ratio (like five parts Winsor orange to two parts permanent rose)
The consistency (tea? double cream? a tint?)
That consistency language is something watercolor artists talk about all the time, and seeing it built right into the tool felt thoughtful. It's clearly made by someone who actually understands how we work.
The Painting Subject: Strawberry Daifuku
For my test painting, I chose a strawberry daifuku — that Japanese mochi with red bean filling and a whole strawberry inside. It's got pink, yellow, red, and brown, which gave me a nice range of colors to test the app's suggestions against.
My paper was Arteza cold press professional watercolor paper, and I painted without a sketch, as usual.
What the App Taught Me About Mixing Red
This was my favorite discovery of the whole session. I would normally have just grabbed a red straight from my palette and called it a day. But when I tapped the red area of my daifuku photo, Undertint told me to mix permanent rose and Winsor orange — five parts orange to two parts rose — at a creamy consistency.
I mixed it, tested it on a scrap, and honestly? It was a really beautiful red. Warmer, more alive than what I would have pulled from the tube. That alone made the whole experiment worth it.
Following the App's Suggestions (Loosely)
Here's the honest truth: I said I was going to mix all my colors in advance the way the app suggested, and then I absolutely did not do that. That's not how I usually work, and old habits are persistent. But I did use the app throughout the painting to check in on specific color areas, and it was genuinely helpful as a guide — especially when I was figuring out the yellows and browns.
Some of the suggested colors weren't in my particular palette (my Winsor & Newton set is missing a few, like permanent magenta and indanthrene), so I made substitutions. When the app offered multiple match options with a percentage rating for how close each would get me, I'd look for suggestions that used colors I was already working with elsewhere in the painting. Keeping a limited palette cohesive is always the goal — if I'm already using permanent rose somewhere, I'd rather use it again than introduce a new pink.
Painting the Daifuku: Layer by Layer
The strawberry: I started with my mixed red, keeping things loose and focusing on the general shape. I wasn't worried about the seeds yet. Once the first wash dried (I live in the Pacific Northwest, and it was a damp day — even the blow-dryer took forever), I came back in with the same red mix. Watercolor dries paler, so you can always re-apply the same color to punch things back up. For the seed pockets, I kept things very minimal — I dotted some marks along the surface in loose rows, because strawberry seeds aren't completely random; they do tend to run in lines.
The mochi wrapper: For the texture of the rice flour coating, I used dry brushing — not a very wet brush, held on its side, dragged lightly across the surface. Since watercolor is a subtractive medium and you paint in shadows rather than painting the light, I tried to leave the high points of that floury surface unpainted and only suggest the texture in the mid-tones.
The red bean jam: The app suggested burnt umber for the jammy filling, which made total sense — red bean really does read as brown in person. I dropped some burnt umber into the jam areas and mixed it into the existing reds where the two met.
The shadows and cast shadow: To darken without introducing too many new colors late in the painting, I mixed what was already on my brush. The cast shadow under the daifuku used a touch of the red from the strawberry blended in, which kept it warm and made the whole thing feel connected.
Finishing Touches: Gouache Seeds and a Sea Sponge
For the seeds, I used white gouache mixed with a little yellow — because real strawberry seeds aren't a clean white, they're usually more of a pale yellow-green. I used a very fine brush and placed them loosely in rows, then smudged a few to keep it from looking too precise.
For the rice flour texture on the mochi, I tried something I hadn't done in years: a sea sponge dipped in white gouache. I tested it on a scrap piece of paper first (I recommend doing the same), then applied it sparingly in just a few key spots. The key with sea sponge texture is restraint — if it's everywhere, it reads as messy. Keep it targeted and it adds exactly the kind of organic, subtle detail that makes a painting feel tactile.
My Overall Take on Undertint
I'm not an app reviewer, and I want to be upfront that my palette wasn't a perfect match for the preloaded Winsor & Newton options since I've swapped things around over the years. But even working around those gaps, I found the app genuinely useful — and I think it would be especially valuable for newer watercolor artists who are still building their intuition for mixing.
The biggest thing it gave me wasn't a formula — it was a way of thinking. Instead of reaching for a tube red, I thought about what combination of colors would get me closer to what I was actually seeing. That shift in approach is worth a lot.
Undertint is now out of beta and available in the App Store.