Can I approximate a hex colour using red, blue and yellow?

January 9, 2025 6:03 PM

I have a small set of speedball inks for linocut printing. It includes red, blue, yellow, white and black. If I want to get close to a known colour by mixing those colours, is there a way to approximate how much of each ink to use?

Take, for example, MetaFilter blue, which I think is 006699 in hex. Is there a way to know how much ink to mix to make MetaFilter blue? Based on kindergarten colour theory, those are the primary colours and I should be able to do it. And presumably some semblance of ”you can use these to make other colours” is why speedball sells its beginner printing set with exactly those colours in it? But do I have to do it by eye or is there math?

posted by jacquilynne to Media & Arts (6 answers total)

you might be able to use this to get percentages of color (i.e. the 46% blue, 29% cyan and 25% black it's showing), depending. i don't know how you'd go about getting the percentages to make the 29% cyan but you might be able to approximate that with the same tool.
posted by koroshiya at 6:17 PM on January 9

RGB is additive -- if you mix everything, you get white. Pigments are subtractive -- if you mix everything, you get black. So it's not directly comparable, but I'm sure someone could create a web calc type thing. However, it would require the exact parameters of the pigments you're going to use, as every pigment is different. I don't think this is automate-able.
posted by Rhomboid at 6:21 PM on January 9

Seconding what Rhomboid said about additive versus subtractive color. If your pigment blue is phthalocyanine blue (red shade) it would be a close match to projected Meta Filter blue. A French (red shade) ultramarine also might work. But you would not be able to add different reds and blacks to your set blue to match projected light of MetaFilter blue, the pigment mixture would be relatively muddy and dark after drying.
posted by effluvia at 7:48 PM on January 9

Easiest way is to attempt the mix using single drops.
Once you've got the number of drops roughly right, you can make a bigger batch in the same proportions.

You cannot make all the available colours with those, eg you can't make hot pink, but you can get close to metafilter green probably.

https://janeblundellart.blogspot.com/2014/11/mixing-document-inks.html
posted by Elysum at 8:22 PM on January 9

I would start with throwing the hex at a hex-to-CMYK converter, and trying with the percentages it spits out, with just drops. CMYK is not quite blue, red, yellow, black, of course - it's cyan, magenta, yellow black; but it'd give you a starting point. You could also try using the white to get the red closer to magenta and the blue closer to cyan, if they're very different.
posted by sailoreagle at 5:38 AM on January 10

This varies so much from paint to paint because they have different opacities and underlying tones. To truly match colors you'll need cyan and magenta instead of red and blue, as primary red has yellow in it, and primary blue has red, so they tend to make muddier colors when combined.

You'll just need to experiment with the actual paint you have and see what you can come up with. There's a reason artists spend a lot time learning to mix paint :)
posted by ananci at 7:58 AM on January 10