I've noticed today that memos that are disabled look identical to memos that are not disabled. I observed it with several skins and believe the problem lies with the control rather than the skins themselves. I can give you a screen grab if you want but this should be easy to repro – put an edit, combobox, dateedit and memo on a form and set them all to be disabled – all the controls are 'greyed out' except the memo and the form looks inconsistent, which is about how my program appears right now 😉
EDIT: Actually I think the border is changing slightly but the background color does not, which is the essence of this report. Also it is worth noting that in my app I don't have text in the memo when it is disabled, which means the change to the text color is not an effective indicator.