Why does one light blink after installing new three way switches in my hall?
Likely you have CFL bulbs and no white wire ground.  If this is not your problem, it's somebody's problem who might read this.

The small leakage current through the lighted switch is enough to drive the CFL crazy.  Replace the CFL with a dimmable model, that might help.  Another brand might help.  Or maybe herbs and chanted words and some form of ceremony will make the flicker go away, hard to say.

Or find a lighted switch with a neutral connection that sends no current through your bulbs.
Or get some nice glow in the dark paint and put the regular switch back.