I really love the shading in this piece! The play of light and dark looks really flawless, and I like how you've even got almost purple tones in the shading on the orange and yellow - it makes the layers pop that much better. Overall, very nicely done!
If you're looking to get a more "depressing" color scheme with warm colors, I might suggest staying away from pinks? Reds, oranges, and a little yellow might work better, as pink tends to look naturally cheery.