Hi again
Thank you, I have played round with Marquee effect and yes I can get the result I want (and more). Was just exploring Xlights to see what I could do myself rather than using the excellent library of effects.
I have attached a pic of two headed arrow (as I described it) bottom right of pic. It was the block of alternate on's (Blue/white) I was trying to shorten.
I am on Windows 10. Have now experimented and set smaller timing marks. So will carry on learning and having fun.
Thank you.