In an M4 GBB, choosing the right gas is not simply a matter of using “Green Gas in summer and Red Gas in winter”. Three elements work together: ambient temperature, gas pressure and power adjustment. When one changes, it affects the behaviour of the others. 

The reason is simple: gas pressure increases with temperature. Therefore, the same gas can provide correct performance on a cold day and considerably increase power when the temperature rises. In fact, manufacturers such as NUPROL classify their gases precisely according to pressure and use: 2.0 as standard, 3.0 for cold conditions and 4.0 for systems with heavy bolts and higher pressure requirements.

1-TEMPERATURE

This is the first factor we need to consider. In cold conditions, the available pressure decreases and problems such as cooldown, incomplete cycling or reduced bolt response appear sooner. In hot conditions, the opposite happens: pressure increases and muzzle power may also increase. 
That is why there is no single perfect gas for the entire year. 

2-GAS PRESSURE

As a practical rule, always start with the lowest-pressure gas that allows your M4 GBB to function correctly. 
At moderate temperatures, standard Green Gas is usually the logical starting point. When the temperature drops significantly, it may be necessary to switch to a higher-pressure gas to maintain reliable cycling. Simply using the most powerful gas available is not an upgrade: it increases stress on the mechanism and can unnecessarily raise the joules. 
And be careful about applying this rule without further consideration to an original Tokyo Marui MWS. Marui specifies its own lower-pressure gases for the M4A1 MWS, such as Gun Power HFC134a or Non-Freon Gun Power. 
In short, you will find plenty of charts online and plenty of brands, but you will generally be moving between these 8 kg to 14 kg ratings, with or without silicone. Which one you use will depend on your environment (ambient temperature, game rules, etc.). You are going to have to buy several gases and test which one works best for you. Accept that reality. 
But this video from Papelpalpan, a very good one by the way, will help point you in the right direction. 

 3-NPAS: THE OTHER PART OF THE EQUATION

This is where an especially useful advantage comes into play on an M4 GBB prepared for it: the NPAS or equivalent nozzle adjustment system. 
These systems allow you to adjust the amount of gas used to propel the BB and therefore regulate power without relying exclusively on changing gas. In the SECUTOR CENTURION MWS, for example, we find the Enhanced Drop-In Complete MPA Nozzle Set Gen.2 by Angry Gun, which allows power adjustment using an Allen key. Angry Gun specifically defines it as Muzzle Power Adjustable. 

This allows for a much more logical combination: in cold weather, you can use a gas with enough pressure to cycle the bolt correctly and then adjust the NPAS to keep the power within the field limits. 
An interesting video about valves and how magazines should be filled.