Choosing DX transparency color?

How can I pick the color I want to be transparent in my sprites besides black? I've seen people that have white backgrounds, and they must have chosen white as their transparent color. It has something to do with .low and .high so what do I set them as? Thanks.

In 8, 24 and 32 bit colour mode, set them to RGB(255, 255, 255), which is pure white. In 16 bit I'm not sure what you're supposed to set it to...

I think the easy way to do this across all color modes is to get the value of the pixel located at 0, 0 once you load one of your images and use the returned value as your color key.

VB Code:

'...............................................................
Dim ck as DDCOLORKEY, lngTransCol as Long
 
' create surface and load picture that uses desired trans. color
Set surfOut = DD7.CreateSurfaceFromFile(pFile, ddsd)
 
lngTransCol = GetPixelColor(surfOut, 0, 0)
 
ck.low = lngTransCol
ck.high = lngTransCol
 
'......................................................
 
Public Function GetPixelColor(pSurf As DirectDrawSurface7, pX As Integer, pY As Integer) As Long
Dim rEmpty As RECT
Dim ddsd As DDSURFACEDESC2
 
    pSurf.GetSurfaceDesc ddsd
 
    ' lock the surface to gain direct access to memory
    pSurf.Lock rEmpty, ddsd, DDLOCK_WAIT, vbNull
    
    ' get the color value of the pixel
    GetPixelColor = pSurf.GetLockedPixel(pX, pY)
    
    pSurf.Unlock rEmpty
 
End Function

It worked, thanks guys.