Debbie,
It sounds like he was perhaps a soldier in the British Army rather than in the colonial forces. He might have returned home, left the army and then returned to South Africa.
There's no chance you have any initials??
As there are not too many people of that surname, it would be feasible to go through the soldiers papers either on line or at the National Archives to see if the biographical information they contain matches other information you have.
You may be in luck. In the surviving service papers for those men with the surname Apps and a birth year of 1870 +/- 10 years are two men from Redhill:
APPS, Edward George. Born : 1860. Addess: Cornwall, Cornwall
APPS, James Edward. Born : 1861. Addess: Maidstone, Kent
APPS, William. Born : 1861. Addess: Brenchley, Kent
APPS, George. Born : 1866. Addess: Hastings, Sussex
APPS, William. Born : 1867. Addess: Brenchley, Kent
APPS, Leonard. Born : 1868. Addess: Birmingham, Warwickshire
APPS, Alfred Albert. Born : 1869. Addess: Tunbridge, Kent
APPS, James Martin. Born : 1869. Addess: Redhill, Surrey
APPS, James Larking. Born : 1871. Addess: Maidstone, Kent
APPS, Richard. Born : 1871. Addess: Maidstone, Kent
APPS, Frederick. Born : 1872. Addess: Tenterden, Kent
APPS, Albert. Born : 1873. Addess: Hythe, Kent
APPS, Alfred. Born : 1873. Addess: Hastings, Sussex
APPS, Leonard. Born : 1873. Addess: Sheerness, Kent
APPS, Robert John. Born : 1873. Addess: Maidstone, Kent
APPS, Robert John. Born : 1874. Addess: Maidstone, Kent
APPS, Thomas. Born : 1874. Addess: Tunbridge Wells, Sussex
APPS, Arthur. Born : 1875. Addess: Maidstone, Kent
APPS, John. Born : 1875. Addess: London, Middlesex
APPS, Thomas. Born : 1875. Addess: Redhill, Surrey
APPS, Edward. Born : 1876. Addess: Maidstone, Kent
APPS, Edward. Born : 1876. Addess: Maidstone, Kent
APPS, John. Born : 1876. Addess: London, Middlesex
APPS, William. Born : 1876. Addess: Taunton, Somerset
APPS, Ambrose Edwin. Born : 1878. Addess: Lydd, Kent
APPS, Edward Russell. Born : 1879. Addess: London, London
APPS, Frederick. Born : 1879. Addess: Hastings, Sussex
APPS, Fred. Born : 1880. Addess: Lydd, Kent
These papers are available via FindMyPast or at the National Archives.
Regards
David