The best replacement for transparent is opaque.

The best alternatives to transparent are rated as following:
★★★★★  opaque
★★★★  translucent
★★  semi transparent stain
★★  clear
★★  opaque watercolors
★  routed firewall
★  semi transparent stains
★  transparent
★  solid stain
★  opaque paint
  opaque airbrush paint
  semi transparent
  audioquest
  nordost
  solid color stain
  opaque airbrush
  semitransparent
  semi solid stain

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Speaking about transparent, one probably shouldn't forget about paint.net.

Other search terms related to transparent and their ratings are:
★★★★★ paint.net
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Google Trends

Scale is based on the average worldwide traffic of transparent in all years. Click on graph for more.
transparent
opaque
translucent