4 Reasons:
𝐌𝐚𝐫𝐤𝐞𝐭 𝐃𝐨𝐦𝐢𝐧𝐚𝐧𝐜𝐞
The single biggest reason for the sea of blue is the market dominance of two manufacturers: Dongfeng and FAW.
→ Dongfeng, one of China's largest truck makers, has used a specific shade of sky blue as its corporate colour. Since they hold a massive share of the market, their default colour has become the default colour on the roads.
→ FAW trucks are another giant in the market, and they also very commonly use blue as a standard colour, often a darker navy blue.
𝐋𝐨𝐰𝐞𝐬𝐭 𝐂𝐨𝐬𝐭 & 𝐐𝐮𝐢𝐜𝐤𝐞𝐬𝐭 𝐃𝐞𝐥𝐢𝐯𝐞𝐫𝐲
When logistics companies or individual owners buy these trucks in bulk, they often opt for the standard, no-fuss colour to save cost and time.
𝐁𝐞𝐭𝐭𝐞𝐫 𝐑𝐞𝐬𝐚𝐥𝐞 𝐕𝐚𝐥𝐮𝐞
Also a truck in the manufacturer's standard colour is easier to sell on the second-hand market
𝐋𝐢𝐜𝐞𝐧𝐬𝐢𝐧𝐠
Historically, trucks used to be required to have their license number painted on the side in large, white characters. A blue background provides excellent contrast for this white lettering, making it highly legible for traffic cameras and police. (While this specific rule has been relaxed for newer models, the legacy and practicality remain).”
𝐂𝐨𝐧𝐜𝐥𝐮𝐬𝐢𝐨𝐧
In summary, the dominance of blue trucks in China is due to a powerful combination of the market dominance of manufacturers, industry practices, and practical economic considerations.
So, there you have it.
In future, if someone asks, "why are all the trucks blue?", you can now roll out the answer like a China old hand.