It's because the colour yellow promotes good memory! Writing your to-do list down on a yellow post-it makes you more likely to remember it. The same applies for writing notes on yellow paper, or using a yellow highlighter in your textbook.

Does yellow paper improve memory?

She said that research shows yellow paper with black text is an effective tool with helping memory.

What color helps with memory?

Red boosted performance on detail-oriented tasks such as memory retrieval and proofreading by as much as 31 per cent compared to blue. Conversely, for creative tasks such as brainstorming, blue environmental cues prompted participants to produce twice as many creative outputs as when under the red colour condition.