add warning for incorrect color keys and update documentation

README.md

@@ -317,6 +317,18 @@ local colors = require'catppuccin.api.colors'.get_colors() -- fetch colors with
 catppuccin.remap({ Comment = { fg = colors.flamingo }, })
 ```
 
+#### Overwriting colors
+
+Colors can be overwritten using `vim.g.catppucin_override_colors`:
+
+```lua
+vim.g.catppuccin_override_colors = {
+  base = "#ff0000",
+  mantle = "#242424",
+  crust = "#474747",
+}
+```
+
 #### Hooks
 
 Use them to execute code at certain events. These are the ones available:

lua/catppuccin/core/palettes/init.lua

@@ -12,6 +12,12 @@ function M.get_palette()
 		for k, v in pairs(vim.g.catppuccin_override_colors) do
 			if palette[k] then
 				palette[k] = v
+			else
+				vim.api.nvim_echo(
+					{ { 'Warning: "' .. k .. '" is not a valid catppucin palette color.', "WarningMsg" } },
+					true,
+					{}
+				)
 			end
 		end
 	end