I have never tried knitting. However, I did cross-stitch and embroidery years ago, and developed an interesting technique. I don't know if it could be applied to knitting or not, but here it is, just in case!

Often, I would create my own cross-stitch patterns instead of using a factory-printed one. While trying to cross-stitch a scene from a photograph one day for a gift, I needed a color for the roof of a house that didn't exist in my rather large collection of cross-stitch floss. (The shingles on the roof weren't quite gray, and weren't quite brown.) So, I took a strand of two different colors and put them on the same needle and did the stitching. From a normal viewing distance, the two shades blended, perfectly, into the exact effect I needed!

Could this technique be something you could use? By the way, I really like that painting, too! It is wonderful! 😊