I've decided I hate NATO straps. Too much bulk and extra strap to fuss with.
I love RAF and 3 ring Zulu straps on the other hand. Of the colors out there I usually rotate between black, tan, and grey depending on my attire (bracelet goes on for formal events or meetings).
This thread will be on the topic of grey. Most of the offerings are a variation of a light grey or blue-grey. The exception is the dark blue-grey known as "admiralty grey" as per the original G10 strap for the Royal Navy which is now known as the "NATO". You can get this strap from Phoenix who supplies them to the MOD, but again I don't like natos.

.
Enter the Rit dye.
I've done lots of rit dye projects on polymer gun parts so i said what the hell lets dye a Zulu strap and see if we can get close.
What you need:
Pearl grey rit dye
Water
Vinegar
Strap of your choice.
Bring water to a boil and pour in 1/8 of the bottle of rit dye. Allow to reboil. Add a smidge of vinegar to help with the setting on nylon.
Submerge strap for a few seconds at a time to judge how the color is taking. Once it's where you want it, run under cold water and let dry.
That's it.
You can use this process with whatever colors you want. Remember you can only dye from light to dark so you can go from black to red. But you can go from light tan to red and so forth.
Here's the result.
L-R: crown and buckle grey NATO, finslayer83 grey Zulu, natostrapco grey RAF.
Attached File
while a smidge darker than the RN Grey - I am thrilled with the result and now want to buy some more colors to mess with.