Since most 和菓子 don't really have much flavour, here are some typical colours and seasonal flavours that could be used for things like 打ち物 etc.

Month Layered Colours (top to bottom) Seasonal Image Flavours
January white, red; why not work some gold leaf into it? auspicious colours for the 正月 I like the idea of using 山椒 here; but orange blossom also feels fine
February white, pale green 雪間の草; or you could add some pink for the 梅 梅・甘酒
March pink, white, green 菱餅, 菜の花 strawberry, peach, rape
April soft yellow, light green 桜 桜, slightly bitter green flavours
May deep green, white, indigo iris and fresh foliage iris (floral), violets
June blue, white, purple hydrangea and rain blueberry, lavender
July indigo, with silver leaf 七夕 night sky 黒蜜, mint
August deep blue, white summer night and moonlight melon, jasmine
September white, purple harvest moon and bush clover chestnut, black sesame, roasted tea
October orange, crimson, dark brown autumn leaves persimmon, sweet potato, cinnamon
November rust red, gold maple and late foliage chestnut, roasted tea, walnut
December white, deep red, dark green winter camellia (or Western Christmas colours) yuzu, red bean, pine