@chugthebones I like the surprising pop of cobalt blue from the really intense lithodoras. (I only recently got these, so i dont know if they'll survive yet, but ive been checking local gardens for typical established plants, and ive seen a few around growing freely)
I'm currently into getting petunias which probably sounds really old fashioned, but they have a really good range of colours and can get some fantastic intense velvet purples and super magenta. They are still in development for a good yellow i think (i bought what were supposed to be yellow, but it looks like the colour of used paint water. There is a yellow that looks like pastel lemon meringue) They also have some weird varieties, and a really good black, polkadot, stripes and contrast bleach tips. (Red and white, acid pink and green, maroon an yellow) There's a white with dark veins that looks like it should be called "the undead" there are just a ton of reds of all kinds and a massive range of pastels. I quite like the cinnamon, which changes colour as time passes, and the underlying magenta shines through. They flower like crazy through the season too.
For a really bright acid yellow and ease of care, there's pansies which also have their own wide colour range.
For intensity, i also like the ruby (magenta) and crystal palace (violet blue) lobelia.
Petunias and lobelia i buy back year by year as they dont survive, but pansies can over winter, but i start discarding when they get tatty.
Nasturtiums can get a intensely fluorescent orange going.