as a enthusiatic member of programs in TRON should have blood,
I propose they bleed a processed form of energy. Their lightlines function similarly to circulatory systems. The color of their energy usually matches their lightlines.
It glows slightly, usually somewhat neon at first. Then as it evaporates/dries, it darkens and eventually leaves a dark grey soot film behind. It’s not the easiest to wash off.
This is definitely not an excuse to draw characters covered in blood/energy, not at all