Blitz not reading in bitmaps properly? Colour prob

My system adds tiles to a texture by reading in a bitmap image, and then to ensure the proper alpha channels it goes through it pixel by pixel, checking the colours using ReadPixelFast.

If the pixel is all black (i.e. $000000) then the game will make it fully transparent ($00), otherwise it will make it fully opaque ($FF).

However, one of my graphics uses $010101 to represent black. Ideally my system will make this fully opaque, yet it comes through transparent.

The code that adds the image to the texture is as follows:

Function E2_editTexture(image, texture, x, y)
	LockBuffer TextureBuffer(texture)
	LockBuffer ImageBuffer(image)
	width = ImageWidth(image)
	height = ImageHeight(image)
	
	For a = 0 To height-1
		For b = 0 To width-1
			colour = ReadPixelFast (b, a, ImageBuffer(image))
			If (colour And $00FFFFFF) = $00000000 Then
				WritePixelFast x+b, y+a, $00000000, TextureBuffer(texture)
			Else
				colour = (colour Or $FF000000)
				WritePixelFast x+b, y+a, colour, TextureBuffer(texture)
			End If
		Next
	Next

	UnlockBuffer TextureBuffer(texture)
	UnlockBuffer ImageBuffer(image)
End Function

I've also noticed in the past that $FFFFFF, which is white, has been coming out something like $F8FAF8 or thereabouts. What's going on that I'm losing values? This means I cannot use black in any of my images, which isn't acceptable.

Any help appreciated.