Flicker issue when rainbow effect is running.what’s the issue? 
Led-ws2812b
It looks like Mark Kriegsman’s rainbowWithGlitter pattern, so the flicker is intentional: https://gist.github.com/kriegsman/062e10f7f07ba8518af6#file-demoreel100-ino-L74-L100
If not, can you share the code you’re running? Post it on http://pastebin.com and give a link to it.
Need more information. Here’s some suggestions of what we need:
In this case, just posting your .ino file on http://pastebin.com should suffice.
@Jason_Coon yes thats the code.
Just remove rainbowWithGlitter from the gPatterns list on line 40: https://gist.github.com/kriegsman/062e10f7f07ba8518af6#file-demoreel100-ino-L40-L100
@Jason_Coon thank you very much
… ( must be shattering for Mark)

This gave me chuckle. I think that’s a first.