Black and white are both hot legs. Green is safety ground. Cords are rarely available in any combination but black, white, and green.
make absolutley sure the unit nameplate says 240 V.

If it really is 220-240V, your outlet's wiring should be black and red hots (or two blacks) and a safety ground green or bare copper. The welder's white and black go to the two hots, the green to the ground (or grounded neutral if you're using an older dryer or range outlet).

Flexible cords aren't usually made in two-hot colors, just the normal black+white for 110V. White and black are treated the same only if you're using 220V. If you want to be completely code, paint the ends of the white wire red or black.

I think I may have figured out why this thing is the way it is, the input is called out as 50 Cycle, that would be our counterparts on the other side of the ocean. this thing being an inverter I think negates the importanc of frequency. A little more research and it may be time for the fire extinquisher and contact closure.

50 Hz equipment typically runs fine on 60 Hz. The opposite is not true.
An inverter normaly converts DC to AC. Are you sure what you have??

Thanks for the input guys, this thing is indeed a TIG/Arc welder. The inverter business is getting kind of cloudy, In my motorhome thay call the AC to DC power inverted or converted. The only thing that remains sacred is that a full wave rectifier is changing AC to DC.

AC to DC is rectified. DC to AC is inverted.
Make sure the welder is a true 240 V only device (some need 120 V also). This will determine if it needs a 3 wire feed (2 hots, normally black and white) and a ground or a 4 wire feed (2 hots, black and red, aand a white neutral). The final wire is always a bare or green safety ground.
WElders get some reflief on wire size based on duty cycle, so if you can post everything on the nameplate you may not need to run the largest wires.

The nameplate data is as follows;
Input 220VAC 60Hz (nameplate) 50 Hz (schematic) 18 Amps Single phase.
weld current DC Tig 130A
DC Arc 90 A
No load Voltage 50
Duty Cycle 35%

I agree with the fact that an inverter takes DC to AC. I did some research and found this statement from Miller ;
Inverter - Power source which increases the frequency of the incoming primary power, thus providing for a smaller size machine and improved electrical characteristics for welding, such as faster response time and more control for pulse welding.
I also looked in a few more places and found that the frequency increase can be in the form of a square wave, Triangle wave (My day that was probably a sawtooth)or can be sinosodial as well.
Johb in MA had implied that the new four wire grounding system didn't use the grounded neutral scheme. What are they doing now adays?
Thanks

These days ranges and dryers use two hots, a neutral, and a safety ground. I think it was in 2001 when they started saying that the 3-prong grounded neutral scheme was frowned upon in new work.

As far as I know Canada has been using the 4-prong setups for decades.

Three wires is still allowed for a straight 240 V load. Many condensers operate this way. A special exception was made for dryers and ranges that had 240 V and 120 V loads that allowed the neutral to act as a ground also. Existing installations may still be used, but new installations are required to be 4 wire. This has been the NEC rule for many code cycles now (back to at least 1999, it was allowed at least until 1984).
Depending on the AHJ, moving a 3 wire receptacle may not even be allowed. Extending a 3 wire is rarely allowed.

On a similar theme but possibly in reverse, I have the same type of problem. I live in Northern Ireland and I have just imported a new RV from over there. It has a 50amp 4 core power supply hookup (120/240V)(black, red, white and green cores). Our supply over here is 230V but only three cores - positive(hot) - brown, neutral - blue and earth - green/yellow. I had assumed that because the RV only has one air conditioner etc that it probably wouldn't have two hots ie be 240V (and had just been supplied with a generic 50amp capable cord) and I was just going to install a transformer in line but of course, after checking the RV side of the connector there are four wires (black, red white and bare) which again I take it the black and red should be fed 180 deg out of phase. Anybody any ideas how I can feed this given my supply type? Could I just use two transformers?

A single transformer with a center tap will create the US style 120/240V system. The transformer you need is 240V, 240V center tap.
You could accomplish it with two seperate transformers, but now you need either a pair of 240V/120V transformers (wored in parallel to the 240V primary side and in series on the 120 V output side to get 240 V back), or a better matched set of 120V/120V transformers (the primary side is wired in series to the 240 V abnd the seocndary is in series again for 120/240 V).
A single transformer setup is safer.