I'm not sure that this can be done with Vegas Pro's native titler. But NewBlueFX's Titler Pro 7 can do this as it has a function to change global title settings in a project such as typeface elements like font, color, etc. There is a trial version.
@Terry-McBride Hi, put all your text on one track, then add Colour corrector to the track header, or add an Adjustment track, Parent - Child that to the text track/s so the colour only changes the text & not any other tracks & add Colour corrector to the Adjustment track,