Tips about how I made the Underwater Wallpaper (see wallpaper).

Underwater 2 - making of - Step 1

Start with blank document. Fill background layer with gradient going from light blue to dark blue.

Underwater 2 - making of - Step 2

In Layer effects, use very large (250px) black Inner Glow, with blend mode = overlay.

 
Underwater 2 - making of - Step 3

In new layer, select very large brush, set color to white and put a single dot.

Underwater 2 - making of - Step 4

Transform layer (Ctrl-T) to make dot width less and height more.

Underwater 2 - making of - Step 5

Move white dot to top of image (so that only bottom half of it is visible) and set its layer blend mode to Overlay.