Changing case of the first letter of words in string

[Bis]

I want to make the case of the first letter of all the words in a 
selected string to upper case. The code

s/\b(\w+)/\u$1\E/g;

enables me to do this for the whole document.

But the string I want to match and operate on is all instances of 
text following the string

SCTN:

as in

SCTN: News Analysis

or

SCTN: Special Report

But when I try

s/(SCTN:\s*)\b(\w+)/$1\u$2\E/g;

nothing seems to change? : (

Bis
--