Does anyone know what shade of paint the silver part is on a yeti outdoor bumper 2017 model, some nice person has damaged mine and driven off.

try searching < touch up paint for Skoda Yeti >  in Google search.

Various companies are listed and although ' search by reg no.' will only likely show main body colour, there are always 'contact us' options

where, no doubt, they will be able to identify the silver bumper colour common to many  of the the various body colours of the Yeti range.