Sunlight loses some of its blue and red light as it crosses the air.

Step 1. Overhead ($90^\circ$). About $81\%$ of the blue and $95\%$ of the red are left: a ratio of $1.2$. The Sun looks white or pale yellow.

Step 2. At $10^\circ$. About $31\%$ of the blue and $77\%$ of the red: a ratio of $2.4$. The Sun looks orange.

Step 3. At $5^\circ$. Only $12\%$ of the blue, against $61\%$ of the red: a ratio of $5.2$. The Sun looks deep red.