I distinctly remember doing this shading with a smudge tool in Adobe PhotoDeluxe. My, but I was a glutton for punishment. I mean, this was Photo-friggin-Deluxe. I remember the 1.x versions being awesome, though, and the 2.x versions being horribly useless and bloated. I also used Aldus Photostyler, which later went on to become Adobe Photoshop 1.0. Some of the early Blue Neon strips are colored in Photostyler too.(VXO (vxo))