Brown isn't necessarily bad. A light oily brown on the plug is actually ideal. If you only had one run how can you say it's hotter than normal? Many things affect engine temp and "way hotter than normal" is too vague to diagnose on the internet. Need to know the exact temp to see if you're in the ballpark, but proper tuning should be done by sound and performance of the engine. I wouldn't worry about the inside color just yet. Follow the manufacturers instructions for tuning or find an engine tuning video on YouTube. It takes practice... an experienced friend would be helpful too.