The title of the question says "personality", but OP clearly said this "colorful" refers to one's physical color (clothing, hairstyle, etc) in his (deleted) comment. So I'll cover both.
Physically colorful (hairstyle, clothing, body paint, ...)
Yes this is acceptable except that じんびつ is a typo. It should be じんぶつ.
But you could just use a loanword カラフル and say:
This may be fine if there is enough context, but it looks a little confusing because it's ambiguous (one colorful character vs. many characters with different colors). If there are many characters with different colors (like Power Ranger), consider 様々【さまざま】な色【いろ】の登場人物【とうじょうじんぶつ】がいます, which is unambiguous.
色が多い ("has many colors") does not work here. Please try to rephrase it and find a better word/phrase using a dictionary. ("lively", "vivid", "cheerful", etc)
Lastly, 文字【もじ】 means character in the sense of "letter", "alphabet", etc.