Hi. Other sources put a B720 9Q-CTD (c/n 18162) belonging to New ACS Air Charter Svce as stored at Kinshasa, along with three other B707-300s. I can only see two other B707s in the photo, so as you say it's a smaller "707", it could be the B720.
Can't lay my hand on a recent pic of the '720 to confirm it's blue, so hope the above is of use
Cheers