I can't say I've noticed it but this seems to be the norm for many TV ads. There are rules obviously and I'm sure they abide by them.

As to text and background colours there are even rules that apply to those but it has been well know and proven that White on Black is one of the better combinations.

Here's the BCAP guidance notes all 12 pages



  BCAP_Advertising_Guidance_Notes_1.pdf (Size: 293.79 KB / Downloads: 311)