Ship camouflage in general is a subject that requires some background before you'll be able to get a satisfactory answer. The purpose of camouflaging a ship is not to hide its existence or location, when underway a ship produces a distinctive cloud of steam and smoke from the boilers and leaves a wake behind which is very visible from the air. The purpose of camouflage is to make it harder to identify characteristics about the ship, either to disguise its nature or to disguise the exact details of its position - namely heading relative to an observer, a necessary piece of knowledge to accurately bring fire to bear on it. This is usually achieved by painting geometric forms on the ship which will serve to obscure the geometric details on the ship and make it harder to distinguish its shape against the sea or sky by varying the colour/shade of the segments, Bismarck for instance sporting for some of her life a set of high contrast black and white vertical stripes on the bow and stern designed to foreshorten the bow to an observer and throw off estimates of her bearing by making her appear at a sharper angle than she was.

In this case you'll have a hard time judging the effectiveness of her camouflage scheme without firsthand sources recounting attempts to attack the ship, as it very obviously didn't save her from USN aircraft. However, it should be noted that the practice of painting ships with camouflage saw its heyday during WWI and has basically ceased since, Navies instead opting almost unanimously to paint their ships in uniform neutral colours such as greys or blues.

As the art of camouflage applies to Zuikaku, the colour scheme does not appear to have hindered the aim of the USN aviators who attacked her, with reports of a minimum of three torpedo hits up to a maximum of seven, plus up to nine bomb hits. This represents a large number of hits for an attack on a moving warship by aircraft, though the Zuikaku was sunk after three waves of attack, a fourth arriving just after she finally sank.

Sources:
-The Battle of Leyte Gulf: The Last Fleet Action, H. P. Willmott (attacks on zuikaku, reported hits)

Combined Fleet.com opines that it was likely applied during her drydock stint following the Philippine Sea, so the last 2 weeks of July 1944.

Most notably they note that the other 4 carriers which are famous for the 'land pattern' camo also had time to be painted in that time, Amagi and Unryu were completing fitting out and commissioned in the first 2 weeks of August 1944. While Chitose and Zuiho both spent time in drydock either at Kure or elsewhere in Japan in late Summer early Fall of 1944. So plenty of time for them to be finished with work by the time they sortied in October for the endgame at Cape Engano.

The site is run by Anthony Tully, 1/2 of the due behind Shattered Sword and is about as authoritative a free online source you will find. Here is her Tabular Record Of Movements, which is basically a timeline of where the ship was, and what it was doing from her first day to her last.