It sometimes happens when the mods you use are corrupted. You can try opening the .txd file in gta3.img file using an image editor and replace it with the original. Sometimes the mods affects the original txd file as well. Or if the size of the png inside the txd file are bigger than the actual size of mods it happens. Mostly for pd skin mods.
it's like that because your swat character himself is modefied and this vest is modified by it's default = bugged white
i had it the same way when i fully modified my swat character and deleted him cuzz i didn't like how it looked ...So this is your problem
N A T I O N A L O F F I C E O F S E C U R I T Y E N F O R C E M E N T Name: John Gibbins Rank: Federal Officer Badge: 720 Department: NOOSE