Some people see days of the week as colors. The week becomes a stripe across the inner eye. Pick yours.
Grapheme-color synesthesia is the phenomenon where letters, numbers, or units of time consistently appear in color to the perceiver. Day-of-week color association is a related variant. It's more common in childhood and runs in families. The colors are usually stable for a given person across years — your Tuesday is your Tuesday, even if mine is a completely different blue.
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Also worth noting: music can have color associations too. Chromesthesia is the variant where sounds, pitches, or whole pieces of music trigger consistent color experiences. Composers like Scriabin and Olivier Messiaen famously composed with color in mind — Scriabin even built a "color organ" for his Prometheus. If days feel coloured to you, songs and keys probably do too.