The odds can be calculated as a ratio of the number of favorable outcomes to the number of unfavorable outcomes. (Not to be confused with probability, which is a ratio of the number of favorable outcomes to the total number of outcomes.)
Since there are three primary colors, and the cube has 6 sides, there are 3 favorable outcomes and 3 unfavorable outcomes. Thus, the odds in favor of rolling a primary color is `3/3=1 = 100%` .
The odds AGAINST rolling blue or purple would be the ratio of the number of ways to roll anything but blue or purple, which is 4, to the number of ways to roll blue or purple, which is 2: `4/2=2=200%`