I think that for each custom color you select, you should have an option of changing the color of the numbers, borders, and slider-tick circles for that one particular color. This would allow the use of the color white, in addition to very light colors. (The slider-tick circles are the main reason for this, as they're hard to see with most light colors.)
Download: Haruka Tomatsu - Baby Baby Love (TV Size) (palmolive) [palmolive's Insane].osu
Download: Haruka Tomatsu - Baby Baby Love (TV Size) (palmolive) [palmolive's Insane].osu