edit - oops forgot to quote The Soon's question
here.
trivia - TIBS colours were coloured distinctly in pale beige
(some people thought it was white) with yellow and orange
lines. There's a wikipedia pic here

I believe SMRT only painted the front bottom to red (retaining
the black bumpers from TIBS), retaining TIBS's beige colour
for most of the buses. Then side and back of bus they paint/sticker
with SMRT's livery. Also, some buses SMRT only paint/sticker over
the bottom orange/yellow, leaving the body beige colour
intact. Plus over the years of usage and cleaning it becomes like
"dirty beige colour".
Only when the OC500LEs come then the front is truely white.
Actually the livery is stickered, if you notice the 0405s and
the 0405G(non habits) back of the Mercedes Benz badge.