what color represents each line in the navkar mantra

There is no single universally fixed color for each line of the Navkar Mantra across all Jain traditions.

However, in common Jain symbolic practice, the five supreme beings are often associated with these colors:

• Arihant — White
• Siddha — Red
• Acharya — Yellow
• Upadhyaya — Green
• Sadhu — Dark blue / Black

If you mean the 9 lines of the full Navkar Mantra, then different traditions may assign colors in different ways, but the most commonly accepted symbolic color system is for the five Parameshthi, not a strict line-by-line rule.