70's Zenith

Thanks for the people that have helped with my zenith chromacolor. I sometimes get normal color. Picture is always sharp but most of the time color is just yellow, sometimes things that are suppose to be red are actually blue. But most of the time there is no real color. When the color is normal it is great. I have taken the advice and have reset the end of the tube but nothing helped. What else can I do. I love the set and would like to get consistant normal color. Help. Mark