Since you don't say how you are doing it I don't know if these are any easier:
1. Make them out of slabs (you will need to make new materials for the different colored glass) and save the results as a library part (of window subtype).
2. Create as a an image file in Photoshop, Painter, Canvas, etc. (with transparency) and apply as a texture to the window glazing. You will need to adjust the texture size in a new material and the origin (Edit > Align 3D Texture) to get the right fit.