Bit strange as Foster Yeoman is owned by Aggregate Industries Limited, as from June this year. AIL's corporate livery is a mix of white, blue & green. There was a pic in a rail mag recently showing what a 59 would look like if it was painted in new livery. We will just have to wait & see.
Btw, Mendip Rail is an independent freight operating railway company. It's composed of the rail-operation divisions of Foster Yeoman and Hanson Aggregates (previously ARC). Whether this will continue, or whether AIL will run their own trains independantly is anyone's guess at the mo.