Automatically filling % of rows in Pivot Table

Hi,
I am looking for a way to solve the following problem:
I have a pivot table with a row count of around 1000 (filtered). I need a function that would let me pick a random% of them (let's assume 50%). Then, from randomly selected 500 lines, I need to randomly assign them to 5 groups - (Blue, Yellow, Red, Green, White). However, each group must have the same number of members. After searching the internet, I found a lot of information on how to choose a random number, but the key in my case is to work on one document and not change anything (except possibly adding some columns and this forumula). I'm not willing to select 500 rows and then paste them somewhere to continue work, it cannot be done that way.
Thanks in advance for any help in solving the problem!