java - Reverse opposing colors

Question

I have a user setup where they can choose the colors of the alerts. the Alert is the background color on a text or button. But the problem comes in that if they select a dark blue and we have black letters the contrast isnt enough and you cannot read it.

I have tried to make a function to get the reverse opposing color but havent got too far.

Is there such a function?

Answer 1

Use complementary color:

Algo is simple, substract each color component from 255 to get new color components

Color textColor = Color.rgb(255-Color.red(bgColor),
                         255-Color.green(bgColor),
                         255-Color.blue(bgColor));

----- EDIT (As RGB based complement may not work always --------

These two links are very much helpful and on topic:

http://www.splitbrain.org/blog/2008-09/18-calculating_color_contrast_with_php

http://24ways.org/2010/calculating-color-contrast