Understanding the purple shades indicating the balls to pick from, the probable ball.

A ball will be drawn 50% of the times from the darkest purple shade, 20% of the times from the medium dark, 29% of the times from the lightest shade, and 1% of the time from the non-purple balls.

The shades are placed in that order (meaning, not following the percentages, i.e. the 20% get the medium dark) because we focus on the overall range to select from. Consider the 20% and the 29% as added percentages to the probability of the previous range. That way you have the following ranges of number:

• [darkest shades range]: with the darkest colors, you have fewer balls to select from. Since you have a narrower range, your chances of forming a winning set are higher (because the ensemble of possibilities is reduced). But it’s only likely at 50% that a ball will be coming from those numbers.
• [darkest + medium-dark shades]: chances of forming a winning set decreased (more balls to select from), but it’s more likely that a ball will be coming from that range (50+20 = 70%).
• [all purple shades]: chances of forming a winning set is low (so many numbers to pick from), but it’s very likely that a ball will be drawn from those numbers (50+20+29 = 99%).
• [all balls]: chances of forming a winning set is the lowest. It is certain (100%) and a number will be drawn from the available balls in the urn.