Depending how vivid your scarlet is: You can go with white or cream so it really is the accent wall and nothing is shouting for equal attention You can also go for a muted grey or beige

Well for windows and doors you'd use gloss or satin finish paint in white and it shouldn't really be different to your white wall paint in colour , if you used the same shade of white from the same company.

A picture is worth 1,000 words of advice at Houzz. Please comment here and use the Attach Images button to add pix of the space where you have the dilemma. Do you have an inspiration picture, piece of art, rug or fabric that is determining the color for each bedroom or are you just grabbing these colors out of a hat? White goes with all of them.

I'm curious as to why you are choosing a black mosaic without having a plan for the rest of the space, or have you moved into a space with an existing black floor? I think it would be hard to keep clean, since with mosaics there is a lot of grout. For a jewellery store, it's important the goods for sale are presented in an elegant way. You really must consult an interior designer to put a plan together for you which will also include a lighting plan to highlight everything.