M,
Apparently some units did wear the white uniform in the Peninsular, though can't help much with which regts beyond the standard "white issue" listing of: 3rd/13th/14th/15th/16th/17th/18th/21st/32nd/33rd/46th/53rd.
Considering the usual problems associated with uniform supply and the fact that the white was replaced with blue as it wore out, it was highly probable that there was a mixture of white and blue within the same regt or batt.
So if you wanted you could even paint a couple of companies in white and the rest in blue!
DB