Depends how you are going to colorize the image. I am[ no expert, there are Gimp users around who do great work.
This using the gimp_gmic_qt plugin http://www.gmic.eu There is a Windows installer. One of the filters is a photographic colorize, which takes an overlay of color swatches.
I tried taking a small sample, a select & copy, of your paving and used the clone tool which will paint a pattern, In this case like this + other colours.
In gmic
And the result, the cobbles not as good as hoped for but maybe with a little more effort...
This using the gimp_gmic_qt plugin http://www.gmic.eu There is a Windows installer. One of the filters is a photographic colorize, which takes an overlay of color swatches.
I tried taking a small sample, a select & copy, of your paving and used the clone tool which will paint a pattern, In this case like this + other colours.
In gmic
And the result, the cobbles not as good as hoped for but maybe with a little more effort...