Will the colour of my teeth match after a gum lift (gingivectomy)?

The color mis match will be minimal if any. The tooth area that is covered with gum tissue might be lighter in color if you teeth have yellowed/ stained over time. Bleeching could help however , as you have been told , complications might happen. Roots of the teeth might become exposed. The roots are yellower in color this can not be changed. ....

It is possible that there can be some differences in the shade of the tooth but the gingival recontouring usually gives instant dramatic improvemnrj while any coloration issue is very minor.  Right now that irea is covered with pink gums.  Color is rarely if ever a problem

The colour discrepancy may or may not be major. It depends on how yellow your teeth are. Regardless, this can be fixed with whitening. However, you need to find a periodontist who will not hit or expose the roots. I have been doing this for over 20 years and have not hit or exposed the roots nor do I know any other periodontist who exposes roots. When this procedure is planned and done correctly, you need not worry about the roots. A non issue to a good specialist. Good luck!