As far as I know, for 3 digit numbers, each number is read out. For two digit numbers, they're read together.
E.g. "Blue Six Five Seven" & "Red Fifty-Two"
Can't find anything in the rules or appendices about a standardised way of saying numbers but it might be useful to read through this: http://wftda.com/rules/wftda-officiatin ... l-cues.pdf
To know what else to listen out for as well