The goal of Color 21 is to drop the colored orbs into columns to create sums of 21. Go over 21 or 'bust' and the column takes damage. Damage a column 3 times and you lose it. The game ends when 5 levels are cleared or all your columns break. Bonuses are available to increase your score, they include,
- Getting a 21 using all the same color orbs - Getting a 21 using all 5 orb slots - Getting a 21 while ending on a star - Getting a 21 using all different colors - Getting a 21 using a pattern of colors
All bonuses are worth 500 and it's possible to get more than one bonus at a time.