message-colors.svg use:

Copy-Paste those lines from the svg file:

$link_color: #(LATESTCOLOR);
$link_visited_color: #(LATESTCOLOR);
//___
$selection_mode_bg: $selected_bg_color;
$selection_mode_fg: $selected_fg_color;
$warning_color: #(LATESTCOLOR);
$warning_fg_color: white;
$error_color: #(LATESTCOLOR);
$error_fg_color: white;
$success_color: #(LATESTCOLOR);
$destructive_color: #(LATESTCOLOR);
$suggested_color: #(LATESTCOLOR);
$question_color: #(LATESTCOLOR);
//___
$drop_target_color: #(LATESTCOLOR);

These lines replaces the corresponding ones in:

~/mint-themes/src/Mint-Y/gtk-3.0/sass/_colors.scss