Bug type palette is not available in Firered and you need to insert the palette manually.
First, open G3T (Gen3Tool)
Head to Item Editor > TM whatever (Skill swap) item.
Note its image offset and palette offset.
Close G3T
Then open NSE to manually insert the palette, iirc it only take a minimal of 40 bytes.
Click Navigate, and write down the image offset and palette offset which you noted before.
Edit the palette color to your liking, maybe light green or rainbow or whatever.
Then click INSERT, do not click SAVE as saving will overwrite the palette you currently edit.
When NSE asks you where do you want to insert the palette to, remember to always edit the END of every offset number to either 0,4,8, or C.
Example : NSE suggests you to insert the palette to 830003.
Edit it to 830004 or 830008 or 83000C
After that, use G3T (Gen3Tool), go back to that TM whatever which you want to edit.
Edit the palette offset to the offset which you have inserted via NSE.