The best replacement for red peppers is green peppers.

The best alternatives to red peppers are rated as following:
★★★★★  green peppers
★  yellow peppers
  pimentos
  chipotle peppers

Your alternative for red peppers is not listed? Suggest!
Speaking about red peppers, one probably shouldn't forget about feta.

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



Google Trends

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red peppers
green peppers
yellow peppers