I have been looking at more paintings and drawings depicting battles in the First Anglo-Dutch War. I especially notice Wille van de Velde, the Elder, work about the Battle of Scheveningen, as he was actually at the battle. I have also looked at works other van de Velde works, and works by Reinier Nooms and van Diest. There is ample evidence that while the English jack should usually be the "Commonwealth Jack", that vanes were typically white with a red cross, and that it was not uncommon to have large white flag at the main, with a red cross, dividing the flag into quadrants.
There is also ample evidence of red and blue ensigns, with very small white fields, with red crosses. They were usually flown at the stern, but it is not unknown for one to be flown at the main.