If order to use fill, you should open image.svg in a text editor, copy the content, and paste it to replace the whole img line.
Then the fill attribute could be applied to the <svg>
Otherwise, you can change it directly in the file if it suits you.
fill shouldn't be applied to an img.
Besides, no need for the colon when you are using a static value. :fill should be replaced with fill
The colon
:is a shorthand for v-bind. Here you can find more information about v-bind: https://vuejs.org/v2/api/#v-bind