I'm using a png wallpaper with 256 colors and some colors are dithered. All colors I use are multiples of 0x11 for each RGB color (red, green and blue).
For example the color #225555 is dithered (it has some pixels of some other color mixed)

I would like to know how can I avoid this. I want my wallpaper to look good (without dithering). Please Help!

My phone: Nokia 3100

Thanks in advance!