Annotation:
真っ赤っ赤 is an emphatic expression to describe how red it is.
Related:
[#9159009] ほら、見て!空が真っ赤っ赤だよ。写真撮っておこうよ。
Tom, what's wrong? Your face is ___.
Perhaps one of these.
bright red
very red
extremely red
Can anyone think of another way to emphasize redness?