How to make a change in the picture width depending on the degree of loading page?

Good evening.

There is a small preloader, which logo should become coloured progressively according to the degree of str - 0% - BW, 100% color. At the moment it is implemented via timeout and the overlap of one block with the background b & W logo with another block with the background in the form of a colored logo. But you need to make the overlap (in the colored block changes width from 0 to 100%) was gradual and came with the download of the page How this can be implemented? Honestly, I was not able to find a concrete example. Found only for display % load the script with the plugin. The site itself.
June 8th 19 at 16:36

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