UNDERTINT

colour mixing for watercolourists

Mix the colour in front of you

Undertint works out the recipe. You paint.

Download on the App Store

Import a photo and see it as paintable colours

Drop in any reference and Undertint groups it the way your eye does — not the way a screen does.

Mix recipes from your own palette

Tell Undertint the brands and tubes on your desk, and every recipe comes from those paints — never a generic chart.

Read the tones before you touch paint

Switch to value mode to see the composition as tonal bands, with a bar showing how much of each.

Tap a colour, get a recipe that works on paperPro

Single-paint matches with Munsell notation come free; Pro adds two- and three-paint mixes and a dilution strip from masstone to bare tint.

Plan with a grid, zoom into the detail

Lay a configurable grid over the simplified image, then double-tap any cell to recover the fine detail you’d otherwise lose.

Why the recipes actually work

Most colour tools think in light. They work in red, green, blue which mirrors the way screens produce colour: by mixing wavelengths. Mix red light and green light and you get yellow. That’s fine for a display. It’s useless for paint.

Pigments work differently. They absorb light rather than emit it. The colour you see is what’s left after the pigment has taken what it wants from the spectrum. Mix two pigments and you’re combining two different patterns of absorption. This is why mixing paint colours is so much harder to predict than mixing coloured light, and why RGB-based tools give you recipes that look right on screen but wrong on paper.

Undertint uses the same colour mixing theory your paint manufacturer uses, and models pigments the way pigments actually behave: as light-absorbing materials with measurable properties. Those properties vary by manufacturer. Winsor & Newton’s French Ultramarine (PB29) absorbs light slightly differently to Holbein’s, and Undertint knows this. The recipes that Undertint gives you are specific to the paints you’ve told it you own — which is the only way a recipe can reliably work.