I think the next SE franchisee should go for using the livery colour to help the customer understand what service that train is, a la SWT. Certainly would be a help at stations served by both high speed and conventional services (sure, a local commuter or enthusiast may understand the difference, but someone on a day trip may not)
I've got some mockups back at home, but I think that 395s would look good in a grey 'high speed' look, showing the customer that it is a premium service. The 375/377 fleets should remain in their blue colours, while the metro fleets would probably be best in a red colour (matches up roughly with the old SWT colours as well).
Obviously if Stagecoach get the franchise we may get this