SetMaskColor needs to be called before you load the image -or- create the image.
If it still doesn't work then two things are likely
1) you're not specifying the correct RGB - ie 255,255,255 (there is no 256,256,256 as the range is 0-255).
2) the white in your image isn't pure white! but nearly white... check if it really is by using a paint package eye dropper tool or by using blitzmax to grab a colour at x,y.
If it still doesn't work then two things are likely
1) you're not specifying the correct RGB - ie 255,255,255 (there is no 256,256,256 as the range is 0-255).
2) the white in your image isn't pure white! but nearly white... check if it really is by using a paint package eye dropper tool or by using blitzmax to grab a colour at x,y.