how do I mask texture only lets thru at spots I wa

Global sprite=CreateSprite()
Global base=LoadTexture("image.png",4)
Global mask=LoadTexture("image1.png",4)
EntityTexture sprite,base,0,1
EntityTexture sprite,mask,0
prepare_texture(mask)
texture_mask_colour(mask,0,0,0,50)

cube=CreateCube()
PositionEntity cube,0,0,2
ScaleEntity cube,6,2,1

It works but not the way I asked for, here:


There are 2 textures on the sprite, base and the mask texture that I put thru:
prepare_texture(mask)
texture_mask_colour(mask,0,0,0,50)

Both textures dissappear, whic is not what I relly want.

Or perhaps I did something wrong here, and I should see the base texture thru the mask?