For jpeg's don't forget to add jpeg to your uses section.

As for transparent colour always use a "pure" colour, on ethat doesn't alter when set to 16 bit mode.

I stick to fuschia for the transparent colour, $FF00FF.

In photoshop I use a "background" colour that is close to the colour of the sprite. For example gray.. Then change the bitmap from RGB to index colours including the "primary colours" this includes fuschia in the pallete. I then select the background colour and replace with Fuschia. That way I don't get fringes of colour surroundingthe sprite.

I find black to be a terrible colour as the transparent colour as you tend to have black in the sprite itself.

Hope it helps.