Bought a Dracaena Janet Graig Limelight about a year and a half ago. It is doing really well, in a bright but not direct sunlit spot. It was a beautiful yellow when I brought it home, but is now a healthy, but regular green plant. Do the nurseries add anything to the soil to make it yellow? Just wondering what happened to the colour.

You are pretty far North, so even your 'part-sun' is probably more shady then FL shade. Here in South FL i see Dracaenas in part sun outside.
Try giving it weak late/early part-sun (2-3 hours) for starters.
My Dracaenas in NJ were doing good in Western part-sun year round.
Generally speaking tropical plants with variegation require stronger light, especially further North.

Thanks for your reply! Will give it a try and hope the bright colour comes back. It was very unusual .