glowing spark plugs

How old are the plugs?

If they are the resistor type, and the resistor has broken down, they may be arcing internally and "lighting up". Consider replacing them.

Compare the plugs bank-to-bank. If they are visibly different colors, check your mixture distribution (clean the carb, check vacuum leaks, etc...). If they are similar and the insulator is bright white, try a cooler heat range.

Personally, I am a big fan of running the coldest plug possible. If you are trying to "read" the plug, you need to get the right heat range first, and then tune the mixture. Running too hot a plug is a common mistake.