did you properly read the previous posts and links? colour, any colour IS the result of surface oxidation at elevated temperature. brushing a weld/HAZ that is gold, purple or blue will result in a shiney colour free finish too- brushing removes this 'thickened' oxide layer
the colour indicates how much oxidation occured- grey is severly oxidized
contaminated argon could be the cause (never experienced it or for that matter even heard of the problem prior to reading about it on forums- cylinder filling is more heavily regulated in the UK). the most common causes are...
- too much heat input (typically begin with 10% less than for carbon steel)
- not keeping the end of the filler within the gas shield, allowing it to oxidize
- arc length too long (heat is less focused as arc length increases meaning more is required thus increasing overall heat input). no longer than electrode diameter, preferably 1/16" or as short as possible
poor torch angles could also contribute- gas flow directed away from weld
it's pretty easy to eliminate shield gas (bad gas, leaks) as the problem- strike an arc, form a puddle and then stop the arc without moving the torch until the post flow stops. the spot weld/tack should be colour free
if the weld is cleaner (better colour) when done without filler then that would point to oxidized filler being the problem
if you post details of machine settings and thickness of stainless used we'll be able to tell you if you're in the ballpark with regards to amperage, flow rates, post flow etc
