Refer to figures. 
According to ICAO Annex 14, the markers used on overhead wires or cables should be spherical red/white or orange/white.

ICAO Annex 14 - Aerodromes 
6.2.5 Overhead wires, cables, etc., and supporting towers

Marking by markers

6.2.5.6 Recommendation.— A marker should be of one colour. When installed, white and red, or white and orange markers should be displayed alternately. The colour selected should contrast with the background against which it will be seen.
 

Spherical markers (often called "marker balls" or "aerial marker balls") are placed alternately in red and white (or sometimes orange and white) along overhead wires, such as high-voltage transmission lines, that cross a river, valley, or are near an airfield. The contrasting colours ensure maximum visibility against various backgrounds (sky, ground, water) to warn pilots of the obstruction.