If I remember correctly, when EWS started to get complaints from customers that they were sub-contracting out the work to other companies, namely Loadhaul, Mainline and Transrail. The customers wanted consistency, it was around this time that some massive yellow beasties stickers were ordered and applied.
This might not be the issue here but there will be some corporate thinking behind it. Plus I quite like the 37'sin colas livery
Alistair