Had same Problem on my white Pc Engine > Cleaned Hu Card Slot wit Isoprpanol Alcohol and colors where back (use a hu card > put "paper" around with Iso Alcohol on top > put in and out).
Also try to check if there is something inside (smal dirt, hairs etc.) and remove that first
Also try to check if there is something inside (smal dirt, hairs etc.) and remove that first

