Make sure thread watcher icon is visible on sites with dark backgrounds.

src/Miscellaneous/IDColor.coffee

@@ -33,7 +33,7 @@ IDColor =
     ]
 
     # Weight color luminance values, assign a font color that should be readable. 
-    rgb.push if (rgb[0] * 0.299 + rgb[1] * 0.587 + rgb[2] * 0.114) > 125
+    rgb.push if $.luma(rgb) > 125
       '#000'
     else
       '#fff'

src/main/Main.coffee

@@ -273,7 +273,7 @@ Main =
       unless /^rgb\(/.test(bgColor)
         s = window.getComputedStyle(d.body)
         bgColor = "#{s.backgroundColor} #{s.backgroundImage} #{s.backgroundRepeat} #{s.backgroundPosition}"
-      Main.bgColorStyle.textContent = """
+      css = """
         .dialog, .suboption-list > div:last-of-type, :root.catalog-hover-expand .catalog-container:hover > .post {
           background: #{bgColor};
         }
@@ -281,6 +281,13 @@ Main =
           background-color: rgba(#{rgb[...3].join(', ')}, #{0.5*(rgb[3] || 1)});
         }
       """
+      if $.luma(rgb) < 100
+        css += """
+          .watch-thread-link {
+            background-image: url("data:image/svg+xml,<svg viewBox='0 0 26 26' preserveAspectRatio='true' xmlns='http://www.w3.org/2000/svg'><path fill='rgb(200,200,200)' d='M24.132,7.971c-2.203-2.205-5.916-2.098-8.25,0.235L15.5,8.588l-0.382-0.382c-2.334-2.333-6.047-2.44-8.25-0.235c-2.204,2.203-2.098,5.916,0.235,8.249l8.396,8.396l8.396-8.396C26.229,13.887,26.336,10.174,24.132,7.971z'/></svg>");
+          }
+        """
+      Main.bgColorStyle.textContent = css
       $.after $.id('fourchanx-css'), Main.bgColorStyle
 
     $.onExists d.head, Site.selectors.styleSheet, (el) ->

src/platform/$.coffee

@@ -460,6 +460,9 @@ $.minmax = (value, min, max) ->
 $.hasAudio = (video) ->
   video.mozHasAudio or !!video.webkitAudioDecodedByteCount
 
+$.luma = (rgb) ->
+  rgb[0] * 0.299 + rgb[1] * 0.587 + rgb[2] * 0.114
+
 $.engine = do ->
   return 'edge'   if /Edge\//.test navigator.userAgent
   return 'blink'  if /Chrome\//.test navigator.userAgent