For my kama, boots and leather goods I used a combo of physical weathering and acrylic/fabric paints. The only real difference between weathering black and weathering any other color is the "grime" colors you have to use. Black or dark colors won't show up, so instead you have to use lighter colors in small amounts. All the sandpapering/fraying/cheese-grater-ing/driveway-dragging stays the same.
For paint, I personally stay away from things that will potentially wash or wear off, since my flightsuit gets thrown in the wash after hot summer troops. Acrylic artists paint such as Liquitex brand, fabric/puff paint found in the craft aisle, or spraypaint work great because they're designed to be permanent. For colors, any kind of gray (ash), tans (mud), red-brown (red dirt), or light brown (general planetary grime) will certainly show. These can be dry-brushed, spattered, sprayed, or stippled on. Let me know if you want more info on how I like to apply the paint!
Whatever you do, though - apply hints of the same colors to your plates, if you can. If your boots get spattered, go for the boot plates/knees/shins as well. You don't have to go all-out on your plates, but if you have grime instead of general wear and fading, keep the grime consistent.