optimizing ->coloured categories(background)

hi there, im here with a question. on my new project i would see some colours 🙂

my categories should all have different background colours when browsing theme. i know that 1 solution may be using “id”. but im now sure how to use them for categoeries.

my idea came while using and playing an old plugin “weighted categories”. with this plugin its possible to show your visitors your cats in different colour…and different size.

how can i modify my cats so, that for example categorie “web” would have a red background, categorie “tools” green… you got the idea.

im not sure what topic i could search, so i decided to start a new post, dont be bad to me.
thx 4 your answers