I understand that the Welsh part can't be as prominent as the others on the flag, I though just the green lining around the white cross and saltire would be enough without overshadowing the other parts (or maybe I'm not noticing something and prominence in this case is something else, I'm not that well versed in heraldry to be sincere)It's not the colours, it's the prominence. England was held superior to Wales. This lead to Henry VIII directly incorporating Wales into England OTL.
The best you can get of a Tudor Flag of England-Wales is below where the green shield stands in for whatever Arms are attributed to Wales.
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