I think the idea here is good, but it doesn't look quite right: your second circle is skinnier than the first one.

There are also several pre-existing weird qualities of the code that I'm going to point out (Not your fault, I just want to call them out as I see them). This code could probably do with a cleanup anyway

From above:

 if (dc1 == 0xf) {
        return;
}

Secret feature to skip the draw? This code seems to be really old, I think it's probably unintentional.

uint8_t strokeColor = (dc1 - 1) & 0x3;
uint8_t fillColor = (dc0 - 1) & 0x3;

This underflows, which was what was causing the dark colour you were seeing. Kinda weird behaviour.

Probably this code needs some real scrutiny and re-writing, but it's complex and people are afraid to touch it so it hasn't gotten any.

@majaha You are right about the size. I gave it a quick fix by aligning the color to the former one. Though I do think it may need a proper rewrite.