Cargo ship's have a lot of hull to cover in paint and one of the considerations when purchasing or refurbishing a ship is which colour to paint the hull.
Grey or Black would be natural choices, like in the navy and many merchant vessels agree:
Others are painted in their company livery, like:
However, some companies are also in the habit of painting their ships in garish colours, such as:
The Pink Containership (which has a female Master, Captain Ebner, believe it or not):
The Yellow Feeder Vessel:
However, even the most gauche of the modern merchant ships would have trouble competing with the "dazzle ships" of World War I. The allies gave up on trying to camouflage the ships with grey or blue paint and instead conceded they could be spotted, and switched the paints function to be so confusing that through a small u-boat periscope it was very difficult for a Germany naval officer to identify the size, type, weight, course or speed of the ship; thus their torpedoes (which then were required to be precisely aimed), missed the target.