Fix wording in the documentation for primary-only colors

docs/getting-started.md

@@ -160,7 +160,7 @@ Color names are case-insensitive, but must match the names of the Material
 Design color palette. Valid values are: `red`, `pink`, `purple`, `deep purple`,
 `indigo`, `blue`, `light blue`, `cyan`, `teal`, `green`, `light green`, `lime`,
 `yellow`, `amber`, `orange`, `deep orange`, `brown`, `grey`, `blue grey` and
-`white`. The four three colors can only be used as a primary color.
+`white`. The last four colors can only be used as a primary color.
 
 If the color is set via this configuration, an additional CSS file that
 defines the color palette is automatically included. If you want to keep things