diff --git a/.gitmodules b/.gitmodules
index 3d765c1..5d6b1fe 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -48,4 +48,4 @@
 [submodule "book/external/Sphinx-Named-Colors"]
 	path = book/external/Sphinx-Named-Colors
 	url = https://github.com/TeachBooks/Sphinx-Named-Colors.git
-        branch = manual
\ No newline at end of file
+	branch = manual
diff --git a/book/_config.yml b/book/_config.yml
index e1f3110..bcd5678 100644
--- a/book/_config.yml
+++ b/book/_config.yml
@@ -19,6 +19,8 @@ sphinx:
   - teachbooks_sphinx_grasple
   - sphinx_image_inverter
   - sphinx_exercise
+  - sphinx_proof
+  - sphinx_named_colors
   config:
     html_js_files:
     - https://cdnjs.cloudflare.com/ajax/libs/require.js/2.3.4/require.min.js
@@ -47,6 +49,7 @@ sphinx:
       tex:
         macros:
           "newcolor": ['\definecolor{newcolor}{RGB}{111, 29, 119}{\color{newcolor}#1}',1]
+    named_colors_custom_colors: {'onlylight':[165,21,160],'lightanddark':[45,180,117,204,158,110]}
   local_extensions:
     apastyle: _ext/
     bracket_citation_style: _ext/
diff --git a/book/_toc.yml b/book/_toc.yml
index fe6582c..89eb15e 100644
--- a/book/_toc.yml
+++ b/book/_toc.yml
@@ -79,7 +79,7 @@ parts:
       - file: external/Sphinx-TUDelft-theme/README.md
       - file: external/teachbooks-sphinx-tippy/README.md
       - file: features/apa
-      - file: features/custom_colors.md
+      - file: external/Sphinx-Named-Colors/README.md
     - file: features/students
       sections:
       - file: external/annotater/README.md
diff --git a/book/external/Sphinx-Named-Colors b/book/external/Sphinx-Named-Colors
new file mode 160000
index 0000000..fda4027
--- /dev/null
+++ b/book/external/Sphinx-Named-Colors
@@ -0,0 +1 @@
+Subproject commit fda40274420c46a05cee1de839ee4726a3816aed
diff --git a/book/features/custom_colors.md b/book/features/custom_colors.md
deleted file mode 100644
index c5ddb7d..0000000
--- a/book/features/custom_colors.md
+++ /dev/null
@@ -1,170 +0,0 @@
-# Custom colors
-
-```{admonition} User types
-:class: tip
-This page is useful for user type 4 and 5.
-```
-
-Within these online books sometimes extra/new colors are wished for. In this page is shown how this can be achieved.
-
-## Using `definecolor`
-
-::::{warning}
-This method only works for $\LaTeX$  colors.
-::::
-
-::::{warning}
-In this case the color remains the same in ligt and dark mode.
-::::
-
-### Code in `_config.yml`
-
-```yaml
-sphinx:
-  config:
-    mathjax3_config:
-      tex:
-        macros:
-          "newcolor": ['\definecolor{newcolor}{RGB}{111, 29, 119}{\color{newcolor}#1}',1]
-```
-
-### Code in content
-
-```latex
-:::{math}
-\newcolor{\LaTeX}
-:::
-```
-
-### Result
-
-:::{math}
-\newcolor{\LaTeX}
-:::
-
-## Using CSS
-
-In this case one has three options:
-
-1. Light and dark mode the same color
-1. Light and dark mode different colors using two color definitions
-1. Light and dark mode different colors using a color filter
-
-### Light and dark mode the same color
-
-::::{note}
-This method has the benefit that the custom color can be used also within html and css elements.
-::::
-
-#### Code in `_static/color.css` 
-
-```css
-:root {
-    --newcolor: rgb(111, 29, 119);
-}
-
-.newcolor {color: var(--newcolor);}
-```
-
-#### Code in content
-
-```latex
-:::{math}
-\class{newcolor}{\LaTeX}
-:::
-```
-
-```html
-<div class="newcolor">HTML text</div>
-```
-
-#### Result
-
-:::{math}
-\class{newcolor-same}{\LaTeX}
-:::
-
-<div class="newcolor-same">HTML text</div>
-
-### Light and dark mode different colors using two color definitions
-
-::::{note}
-This method has the benefit that the custom colors can be used also within html and css elements with automatic changes when the mode changes from Light to dark or vice versa. 
-::::
-
-
-#### Code in `_static/color.css` 
-
-```css
-:root {
-    --newcolor: rgb(111, 29, 119);
-}
-
-html[data-theme="dark"] {
-    --newcolor: rgb(255, 167, 255)
-}
-
-.newcolor {color: var(--newcolor);}
-```
-
-#### Code in content
-
-```latex
-:::{math}
-\class{newcolor}{\LaTeX}
-:::
-```
-
-```html
-<div class="newcolor">HTML text</div>
-```
-
-#### Result
-
-:::{math}
-\class{newcolor}{\LaTeX}
-:::
-
-<div class="newcolor">HTML text</div>
-
-(filter)=
-### Light and dark mode different colors using a color filter
-
-::::{warning}
-This method has the drawback that the custom colors can only be used as a class.
-::::
-
-#### Code in `_static/color.css` 
-
-```css
-:root {
-    --newcolor: rgb(111, 29, 119);
-}
-
-.newcolor {color: var(--newcolor);}
-
-html[data-theme="dark"] .newcolor {
-  filter:  invert(1) hue-rotate(180deg) saturate(1.5);
-}
-
-```
-
-#### Code in content
-
-```latex
-:::{math}
-\class{newcolor}{\LaTeX}
-:::
-```
-
-```html
-<div class="newcolor">HTML text</div>
-```
-
-#### Result
-
-:::{math}
-\class{newcolor-filter}{\LaTeX}
-:::
-
-<div class="newcolor-filter">HTML text</div>
diff --git a/requirements.txt b/requirements.txt
index ff54450..ebf15b1 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -12,4 +12,7 @@ sphinx-image-inverter
 sphinx-thebe ~= 0.9.9
 
 docutils==0.17.1
-sphinx-exercise
\ No newline at end of file
+sphinx-exercise
+
+sphinx-proof
+git+https://github.com/TeachBooks/Sphinx-Named-Colors.git
\ No newline at end of file