You have to understand this: the purpose of a safety vest is to set yourself apart from an environment.
So logically speaking, you can buy both :
- one for in autumn, yellow, since most leafs are orange then and if you where to wear the orange vest, you wouldn't set yourself apart from your environment but you would blend in with it.
- one for in the rest of the seasons : orange.
However, it's more than merely looking at the changes in environment due to seasons, you should also look at multiple other factors :
- the most occurring color in an area : if in one city there happens to appear lots of yellow houses, then you shouldn't wear the yellow vest and vice versa.
- the most common color associated with cyclists in an area : if cyclists tend to wear yellow safety vests more in one area, you might want to consider doing the same, so you can be recognized as a cyclist by others (cars etc.).
- the human eye's sensitivity to colors, as described above.
- colors which are distinguishable amongst the colorblind.
- Reflective inserts Reflective horizontal stripes and arm cover will improve visibility, glue some of them on the back of your vest and/or on the arms.
- follow the regulations