The 3M green rolocs are 50 grit, last a LONG time and are great to get into tight spaces. The only red or brown ones that I've use aren't really for grinding, they seem to be more for soft rust removal or finish sanding. They are thicker and furrier I don't know if they are what you're referring too, but are described as conditioning discs.
JP
Green Corps Roloc
Maroon Conditioning Roloc
JP
Green Corps Roloc
Maroon Conditioning Roloc
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