As a club Rivi use Yellow Line paint for the faceplates and fluorescent red for the kills. After a lot of testing most people found this the best option.
On a personal basis I found the targets at Treetops both easy to find and when shot up, enough contrast left between the now silvery colour of the kill and the yellow faceplate.
With Wendover I found that the white faced targets were more difficult to find (that could have been placement/conditions) and when the kill was shot up difficulty in differentiating the silvery kill from the white faceplate.
Overall I prefer the yellow faceplates and black kill out of the available options. I also think it important that UKAHFT do stipulate the colours to be used to ensure conformity.