How do I create a new column where the values are selected based on existing columns?

How do I add a color column to the following dataframe so that color='green' if Set == 'Z', and color='red' otherwise?

Selecting 1 of 3 colums as value for new column, based on criteria in row

So I have data with the following format

Getting the random rows from the DataFrame with step

As getting the random values can be retrieved by using range(start, stop[, step])