OK just a few things to try maybe is the distribution of light into the other panes and where the light is coming from? some shades are going to let more light through than others and you've demonstrated this well with the contrast of red and purple. I think what I was thinking the other day is are there panels where the light is coming from say glowing more from the red so the colour may bleed a bit but I may be talking garbage. Is something to experiment with but yeah might come out total shit >u>''''''''''''''

ANOTHER is the thickness and the shade of black on the lines. I mean I don't know how realistic you're going for! Panes are usually held together by lead so maybe try using a deep grey as opposed to solid black. Also the thickness of the lines too, varied thickness in an illustration generally looks better if used advantageously (their placement under and on the neck as well as the tip of his mane look great btw, plus the thick outline on the silhouette) so you might want to consider for ~realism's sake~ the make the ones inside the silhouette a little thicker. Course it is stained glass inspired so stick what looks right to you.

I do like how you've made the panes look raised in areas too and is a nice touch c: you may want to revise the placement of them but that goes into light refraction and stuff that I have no idea what I'm talking aboutvhgfsawe