See: https://github.com/gabime/spdlog/issues/595

On line 85 in file sinks/wincolor_sink.h:
back_color &= ~(FOREGROUND_RED | FOREGROUND_GREEN | FOREGROUND_BLUE |
FOREGROUND_INTENSITY);

'back_color' is of type 'WORD' (unsigned short) whereas a bitwise
complement/NOT returns an int. This results in a conversion warning with
-Wconversion enabled.

85:20: warning: conversion to 'WORD {aka short unsigned int}' from 'int'
may alter its value [-Wconversion] back_color &= ~(FOREGROUND_RED |
FOREGROUND_GREEN | FOREGROUND_BLUE | FOREGROUND_INTENSITY);

Possible solution:
We know that the result of ~(FOREGROUND_RED | FOREGROUND_GREEN |
FOREGROUND_BLUE | FOREGROUND_INTENSITY) is always within the limits of
an unsigned short so a simple cast should suffice (correct me if I'm
wrong):

back_color &= static_cast<unsigned short>(~(FOREGROUND_RED |
FOREGROUND_GREEN | FOREGROUND_BLUE | FOREGROUND_INTENSITY));