Hey Augurex! I'm not your probation leader so I hope @
oOIOoMajic doesn't feel like I'm stepping on his toes here!
Blocks in WC tend to be used as their appearance dictates (turnip baskets are baskets full of turnips, a crate is a crate etc.) but there are times when certain blocks can be used to represent other things for example the butcher's bench can be used as knives and tools for a barber-surgeon. With blocks such as weirwood leaves, however, their use is, as far as I know, just as leaves for weirwood trees so seeing them outside of this setting is a little strange. If you're ever unsure whether a block you're using or want to use isn't appropriate then just ask and I'm sure anybody online will be willing to help you out!
If you're wanting to stick with the red theme then sour leaf, fireweed or any of the other red flowers would work just fine. Plants can be kept indoors, they'd just need a reasonable source of sunlight and some diligent watering. Lots of us use potted plants to add interest to interiors so don't worry too much about that.
Hope this helps!