I wanted to make subtitles for a video yellow but its not subtitles that I imported its subtitles from the video I imported is there a way I can do that for vegas pro 20?
Not that I am aware.
... is there a way I can do that for vegas pro 20?
There's one possible way and that is to mask the burned-in subtitles and use a color change FX to change anything white to yellow within that mask. The downside is that anything in the background that is white or near white will also be changed to yellow - the result will likely be awful and unwatchable. Only if all the images behind the masked subtitles are dark to black would there likely be a presentable result.
BTW, I'm currently watching a Netfilx historical doco with B&W footage but the subtitles are white - dumb idea! White on white just doesn't work even with a grey drop-shadow. Yellow subtitles are much better.