[nom]

This! Interpolating in linear RGB space is the biggest issue, I'm sure it will improve a lot simply by using a more suitable colorspace. Triangles might not be noticable at all then, except in extreme cases (which are undesirable anyways).

[grgrdvrt]

I'll try a different color space, for sure, but I think the interpolation method is the real culprit. I have the feeling that in a configuration like this:

  A-B
  |/|
  C-D

the position of D could have an impact on how ABC is rendered.

But I'll try another color space first, it should be easier to implement.