.reg files to create new sessions using the Solarized color scheme which you can modify/duplicate as you see fit.
To copy the color settings into an existing session, edit
solarized_light.reg and replace
Solarized%20Dark in the third line with the name of the session you want to modify.
PuTTY Tray can store sessions in text files as opposed to the Windows registry. To modify an existing session to use Solarized colors, open the file in a text editor and replace the lines beginning with
Colour## (0-21) with the version from