Why the Background Is Red
Indonesia is one of very few countries requiring a coloured background.
Indonesian passport photos use a red background under Imigrasi guidance. Almost every other country in the world specifies white or light grey, which is why this catches people out — a perfectly good photo taken for any other document is the wrong colour here.
The corollary matters just as much: the Indonesian *visa* photo, which foreign nationals upload to the e-visa portal, uses a solid white background. Red is for the passport, white is for the visa. Getting these backwards is the single most common Indonesian ID-photo mistake.