Use of Colors and Chinese Five Elements
Although Causeway Bay Tin Hau Temple is worshiping the Sea, the temple design consists mainly with the element of "fire" and 'wood" rather than the element of "water".
For example, the red ball on the roof means the sun which is always considered as "fire".The green roof means the "wood" element.According the friendship theory of 5 elements (i.e., gold, water, wood, fire, and earth), "wood" can produce "fire".
However, people worried that fire would destroyed the wood structure. Thus, they painted black which symbolized as "water" element closed to the roof.
References:
http://rthk.hk/elearning/architecturetour/images/china/lecture01.pdf
http://lugang.tomio.idv.tw/ogsmall.htm#1313