When the shape is selected in the Titler workspace, Color Properties will be active and you can open it and color your shape.
As I say in my books, you can select a shape you've already drawn by switching to the Selection Tool (the arrow) in the Titles Toolbar and then clicking on the shape.
To follow up Steve's comment on Fill, if you also wish to Stroke the Shape, you will first apply a Stroked Style (from the Style's Library), and can then adjust that Stroke.
If you have a lot of common work, say a reoccurring Shape with both Stroke & Fill, you can Save your Style, and reuse it.
My mistake... OOPS!
I selected a TITLE that must have had a transparent background (BLUENOTES_LWR_THIRD).
I usually start by selecting any TITLE then deleting the default graphics in it to create a black b/g.
From there, I make copies of the b/g and use those for my custom titles (Intro, end, etc.) which I add TEXT to.
Once I selected GENERIC1_TITLE, and deleted the default graphics, I was able to add RECTANGLE to it
and modify the fill color.
I know there's probably an easier/better way to create titles; just haven't had the time to 'explore' more.
Thanks for the quick reply!
If you had one my books you'd know you can by-pass the whole title templates area and start with a blank title just by clicking on the little 'T' icon in the lower right of the Monitor panel rather than going through the Titles panel.