Add auto switching vim colors based on macOS theme

vim/rc/ui.rc.vim

@@ -75,10 +75,6 @@ set notitle
 
 " Function and command to update colors based on light and dark mode
 function! UpdateColors()
-    "If not a mac, let's get out of here
-    if !IsMac()
-        return
-    endif
     " Get the light color or default to VIM_COLOR
     let light_color = $VIM_COLOR
     if !empty($VIM_COLOR_LIGHT)
@@ -89,13 +85,17 @@ function! UpdateColors()
     if !empty($VIM_COLOR_DARK)
         let dark_color = $VIM_COLOR_DARK
     endif
-    " Find out if macOS is in dark mode
-    let cmd = "osascript
-        \ -e 'tell application \"System Events\"'
-            \ -e 'tell appearance preferences'
-                \ -e 'return dark mode'
-            \ -e 'end tell'
-        \ -e 'end tell'"
+    " Detect using an env variable
+    let cmd = "echo $IS_DARKMODE"
+    " On macOS we can do something a bit more fancy
+    if IsMac()
+        let cmd = "osascript
+            \ -e 'tell application \"System Events\"'
+                \ -e 'tell appearance preferences'
+                    \ -e 'return dark mode'
+                \ -e 'end tell'
+            \ -e 'end tell'"
+    endif
     let dark_mode = substitute(system(cmd), '\n', '', 'g')
     " Set colorscheme and background based on mode
     if dark_mode == 'true'
@@ -107,4 +107,5 @@ function! UpdateColors()
     endif
 endfunction
 command! UpdateColors call UpdateColors()
+" au BufEnter *.* call UpdateColors()
 call UpdateColors()