Best high Power RGB Led

i want a rgb led which can EXACTLY display the color that user selects from color dialog box

Then you are stuffed because it can not be done.

Also note that exact colour and perceived colour are two different things because the perceived colour depends on the background.

See also:-
https://www.google.co.uk/search?q=perceived+colour+illusion&hl=en&client=firefox-a&hs=ekq&sa=X&rls=org.mozilla:en-US:official&prmd=imvns&tbm=isch&tbo=u&source=univ&ei=yxiMUNqDF-mp0QXe2YHABg&ved=0CD4QsAQ&biw=1100&bih=637