diff --git a/khal/api.py b/khal/api.py
new file mode 100644
index 000000000..1db9595ee
--- /dev/null
+++ b/khal/api.py
@@ -0,0 +1,3 @@
+from .ui.colors import register_color_theme
+
+__all__ = ["register_color_theme"]
diff --git a/khal/cli.py b/khal/cli.py
index 538ff9d4d..0c6132b34 100644
--- a/khal/cli.py
+++ b/khal/cli.py
@@ -29,6 +29,7 @@
 
 import click
 import click_log
+import xdg
 
 from . import __version__, controllers, khalendar
 from .exceptions import FatalError
@@ -252,6 +253,7 @@ def cli(ctx, config):
             logger = logging.getLogger('khal')
             logger.handlers = [logging.FileHandler(ctx.logfilepath)]
         prepare_context(ctx, config)
+        find_load_plugins()
 
     @cli.command()
     @multi_calendar_option
@@ -512,15 +514,21 @@ def interactive(ctx, include_calendar, exclude_calendar, mouse):
     def interactive_cli(ctx, config, include_calendar, exclude_calendar, mouse):
         '''Interactive UI. Also launchable via `khal interactive`.'''
         prepare_context(ctx, config)
+        find_load_plugins()
         if mouse is not None:
             ctx.obj['conf']['default']['enable_mouse'] = mouse
-        controllers.interactive(
-            build_collection(
-                ctx.obj['conf'],
-                multi_calendar_select(ctx, include_calendar, exclude_calendar)
-            ),
-            ctx.obj['conf']
-        )
+        try:
+            controllers.interactive(
+                build_collection(
+                    ctx.obj['conf'],
+                    multi_calendar_select(ctx, include_calendar, exclude_calendar)
+                ),
+                ctx.obj['conf']
+            )
+        except FatalError as error:
+            logger.debug(error, exc_info=True)
+            logger.fatal(error)
+            sys.exit(1)
 
     @cli.command()
     @multi_calendar_option
@@ -698,5 +706,18 @@ def configure(ctx):
 
     return cli, interactive_cli
 
+def find_load_plugins():
+    """Find and load all plugins in the plugin directory."""
+    # check all folders in $XDG_DATA_HOME/khal/plugins if they contain a
+    # __init__.py file. If so, import them.
+    plugin_dir = os.path.join(xdg.BaseDirectory.xdg_data_home, 'khal', 'plugins')
+    if not os.path.isdir(plugin_dir):
+        return
+    sys.path.append(plugin_dir)
+    for plugin in os.listdir(plugin_dir):
+        if os.path.isfile(os.path.join(plugin_dir, plugin, '__init__.py')):
+            logger.debug(f'loading plugin {plugin}')
+            __import__(plugin)
+
 
 main_khal, main_ikhal = _get_cli()
diff --git a/khal/settings/khal.spec b/khal/settings/khal.spec
index ec4e8eefd..951a169aa 100644
--- a/khal/settings/khal.spec
+++ b/khal/settings/khal.spec
@@ -258,7 +258,7 @@ blank_line_before_day = boolean(default=False)
 #
 # __ http://urwid.org/manual/displayattributes.html
 # .. _github: https://github.com/pimutils/khal/issues
-theme = option('dark', 'light', default='dark')
+theme = string(default='dark')
 
 # Whether to show a visible frame (with *box drawing* characters) around some
 # (groups of) elements or not. There are currently several different frame
diff --git a/khal/ui/__init__.py b/khal/ui/__init__.py
index 806501b43..cb7e222ae 100644
--- a/khal/ui/__init__.py
+++ b/khal/ui/__init__.py
@@ -31,7 +31,7 @@
 
 from .. import utils
 from ..khalendar import CalendarCollection
-from ..khalendar.exceptions import ReadOnlyCalendarError
+from ..khalendar.exceptions import FatalError, ReadOnlyCalendarError
 from . import colors
 from .base import Pane, Window
 from .editor import EventEditor, ExportDialog
@@ -1356,6 +1356,17 @@ def start_pane(
         color_mode: Literal['rgb', '256colors']='rgb',
 ):
     """Open the user interface with the given initial pane."""
+
+    # we can't use configobj to do validation of theme for us, because when the
+    # config is passed, we haven't loaded plugins yet. We could load plugins
+    # earlier, but then logging wouldn't work at plugin loading time.
+    # We do this early, so that logger messages still get shown in a regular way
+    theme = colors.themes.get(pane._conf['view']['theme'])
+    if theme is None:
+        logger.fatal(f'Invalid theme {pane._conf["view"]["theme"]} configured')
+        logger.fatal(f'Available themes are: {", ".join(colors.themes.keys())}')
+        raise FatalError
+
     quit_keys = quit_keys or ['q']
 
     frame = Window(
@@ -1406,7 +1417,6 @@ def emit(self, record):
     logger.addHandler(header_handler)
 
     frame.open(pane, callback)
-    theme = getattr(colors, pane._conf['view']['theme'])
     palette = _add_calendar_colors(
         theme, pane.collection, color_mode=color_mode,
         base='calendar', attr_template='calendar {}',
diff --git a/khal/ui/colors.py b/khal/ui/colors.py
index 5cffb116d..055a56364 100644
--- a/khal/ui/colors.py
+++ b/khal/ui/colors.py
@@ -107,3 +107,7 @@
 ]
 
 themes: Dict[str, List[Tuple[str, ...]]] = {'light': light, 'dark': dark}
+
+
+def register_color_theme(name: str, theme: List[Tuple[str, ...]]):
+    themes[name] = theme