Edit README section concerning themes and color themes

Ref #646

1 files changed, 6 insertions, 2 deletions

diff --git a/README.md b/README.md
index 63b78185..c948a356 100644
--- a/README.md
+++ b/README.md
@@ -427,9 +427,11 @@ All delta options can go under the `[delta]` section in your git config file. Ho
 
 <table><tr><td><img width=400px src="https://user-images.githubusercontent.com/52205/86275048-a96ee500-bba0-11ea-8a19-584f69758aee.png" alt="image" /></td></tr></table>
 
-### Custom color themes
+### Custom themes
 
-A "theme" in delta is just a collection of settings grouped together in a named [feature](#features-named-groups-of-settings). The delta git repo contains a collection of themes created by users. These focus on the visual appearance: colors etc. If you want features like `side-by-side` or `navigate`, you would set that yourself, after selecting the color theme. To use the delta themes, clone the delta repo (or download the [themes.gitconfig](./themes.gitconfig) file) and add the following entry in your gitconfig:
+A "theme" in delta is just a collection of settings grouped together in a named [feature](#features-named-groups-of-settings). One of the available settings is `syntax-theme`: this dictates the colors and styles that are applied to foreground text by the syntax highlighter. Thus the concept of "theme" in delta encompasses not just the foreground syntax-highlighting color theme, but also background colors, decorations such as boxes and under/overlines, etc.
+
+The delta git repo contains a collection of themes created by users. These focus on the visual appearance: colors etc. If you want features like `side-by-side` or `navigate`, you would set that yourself, after selecting the color theme. To use the delta themes, clone the delta repo (or download the [themes.gitconfig](./themes.gitconfig) file) and add the following entry in your gitconfig:
 
 ```gitconfig
 [include]
@@ -445,6 +447,8 @@ Then, add your chosen color theme to your features list, e.g.
     ...
 ```
 
+Note that this terminology differs from [bat](https://github.com/sharkdp/bat): bat does not apply background colors, and uses the term "theme" to refer to what delta calls `syntax-theme`. Delta does not have a setting named "theme": a theme is a "feature", so one uses `features` to select a theme.
+
 ### diff-highlight and diff-so-fancy emulation
 
 Use `--diff-highlight` or `--diff-so-fancy` to activate the respective emulation mode.