No! Regular expressions can only be used for the function list.
But I have a workaround for your problem. Make sure the language is case sensitive - language definition line withoutNocase. Copy following lines to your language.
/C1"Upper case"
** A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
/C2"Lower case"
** a b c d e f g h i j k l m n o p q r s t u v w x y z
This is not perfect, because it simply highlights all words starting with an upper case letter with color 1 and all words starting with a lower case letter with color 2, independent of the case of the other letters of the word. But maybe this will help and is enough for you.
Best regards from an UC/UE/UES for Windows user from Austria