Switching from internal to external for a minute - the livery work in SE has always been mad. Since the 375s and 376s came in connex white/grey with yellow doors, and the Networkers had all been done up in the same way, the first action SE took was to start replacing yellows with blue/lilac, but it wasn't done in any kind of coherent way, so we were left with multiple different blue doors on the 375s, some units had the grey taken off altogether instead of painting dark blue over it, leaving them just yellow and white, some were untouched apart from logos, and some had the full white/blue with lilac door treatment.
The networkers were more consistent externally, and SE did get around to giving all the 465s and 466s the white/blue lilac door livery at about the same time as the Hitachi retractioning. Eventually they settled on using the high speed colours on the 375s, and as we have seen they are now finally approaching homogenous. As for the 376s, they were always the lowest on the list for having an external paintjob because they were the newest and cleanest. Now with TfL looking hungry for them, they won't be touched until they change hands.
The 377s could even be sent for the refresh the 375s are having, which would make them virtually identical, but I think that will be up to the next franchisee.