Hmm, collecting colors through drawing... I am not very well-versed in pigments, but I am curious which colors he can collect when able to draw only black, white and red. And what he will be able to draw with those new colors, to collect further other colors. And so on. For a first step, maybe yellowish colors can be had from drawing foodstuffs that are red (chilli juices are yellowish, right?). When he has brown/yellowish, he can draw kiwis, which are green inside. Think you can extract green color from that flesh? I fact, I think most colors can be extracted once he has brown, and from my experience brown should be easy to get once he can mix multiple colors
Will be interesting to see this kind of dr.stone-esque incremental-game-esque story, where he doesn't even ever need to move away from his drawing surface to further progress.
There have been some artist isekais in the past but the MC being limited by "the degree of completion" is pretty unique. With it, there's a good amount of growth to be had with MC's technical ability and while having the logical limitation of materials. I'm sure that at some point, that limitation is gonna disappear with the MC just recreating his colorset by painting his color set and It does raise the question of why the MC doesn't just draw a white box of gouache or watercolor paints but for right now, it's cool.
I gotta admit that it's kinda refreshing to see the MC not being a genius artist from the get-go and not "I can draw random bullshit from my arse in the air that can insta-wipe bosses" in the 1st chapter. Looking forward to seeing the rest of the story.
They have also almost always been a trashekai in disguise, where the drawing is just a means to an end (OP-tueeee!!!). Here it seems that drawing is the goal (so no travelling, touring, waifuing, etc, if it gets in the way of drawing - well, waifus might appear if he draws them, but they shouldn't be in any more focus than making sure he eats and sleeps and doesn't die drawing until he falls ill from starvation and dies).