The best replacement for watercolors is acrylics.

The best alternatives to watercolors are rated as following:
★★★★★  acrylics
★★  oils
★  pastels
★  . oils

Your alternative for watercolors is not listed? Suggest!
Speaking about watercolors, one probably shouldn't forget about pen and ink.

Other search terms related to watercolors and their ratings are:
★★★★★ pen and ink
You have in mind a companion for watercolors and it is not yet here? Propose!



Google Trends

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watercolors
acrylics
oils