Unfortunately, there is no standardized color code of welding tanks, and therefore gas identification should be made ONLY by the label appearing on it. The gas provider is responsible for affixing the correct label to the tank before you receive it so there is no possibilities of "mixup."
But generally in these parts [East coast]...
Black ~ Acetylene
Green or Orange ~ Oxygen
Brown ~ 100% Argon ~or~ 98/2 - 75/25 mixtures
Dark Maroon ~ 75/25 mixture
The military and certain scientific communities have their own marking systems for their typically used gases that are required to maintain specific quantities of this or that or specific levels of absolute purity for calibration purposes etc.
Tanks that have different rings around them are generally specialty gases and as such don't apply to welding unless specifically required for an extremely critical automated welding process.