Actually, I have no idea how to do a flood fill in Photoshop.
(Aaaargh! That means Atwa has skills that I don't. Somebody tell me quickly, please!)
Step 1. Open Photoshop
Step 2. Select the item you wish to flood fill
Step 3. Select the Paint Bucket Tool (hint; it looks like a paint bucket)
Step 4. adjust the tolerance all the way to 255
Step 5."Flood fill" the item with color or texture (preferably sick-making)
Step.6 Upload to TSR
Step.7 Wait for giddy TSR subscribers to tell you how talented you are.
Step.8 Believe them
Step.9 Repeat steps 1 through 8 until you are "promoted" to Artist Manager