Just a guess, but the backlighting is highlighting the unevenness of the paint. Some areas have heavier paint allowing less light to show through, while thinner coats allow more light to show through. Also there was some bleed under your tape / stencil. On wood, I would first give a light coat of transparent base to seal the edges. On glass, I use rattle can matte clear, but I'm not doing kitchen windows, i'm doing "wall hangings" using repurposed vintage windows. Start with light even coats, gradually building color, using opaque paints, keep the coats kind of "misty"', you're not going for heaviness. Final coat should be overall even coat of under reduced opaque white. This will reduce the color effect when viewed from inside. Remember, I'm doing wall "art" - there is no inside view. Remove your stencils / masking when the paint is dry, but not cured, to reduce "pulling" the paint. Acrylic paint doesn't stick to clean glass and is easily wiped off. Please don't use solvent based paint or you might just be celebrating the holidays longer than expected and spraying solvents in your living space is not recommended... Happy Holidays!!!
PS: I'm guessing that you are painting from inside. If from outside, layers would be trans base to seal, opaque white, then colors
