Although we don't have a Repeat Until/Do While block, people have found ways of doing this manually
This way involves putting code in an ability and it will keep on calling itself while a condition is true:
(This will repeat setting its color to purple while
ValueB = 1. Alternatively you can change the condition to a Not Equals for Repeat Until conditions.)
You could also use a Repeat Forever which continually checks if something meets a condition and stops when it doesn't. Credits to AwesomeCilantro for this!
However, you won't be able to add more code to this rule though, or it won't run.
A while ago, I made a project including these two examples too: