A lot of people talk about color in welds, but don't always get into why color does or does not matter.
On stainless steel(bottom), heavy colors show that an oxide layer has formed, which can effect corrosion resistance. That can be cleaned off(mechanically or chemically). It doesn't necessarily mean the weld is bad. If it's super bright, you *may* be welding too cold. If it's a dull grey, you *might* be too hot.
But on titanium(top) the big deal is that at elevated temps, the material sucks in contaminants in the absence of shielding gas. These contaminants will actually effect the integrity of the weld. Titanium gets pretty colors when it's at those elevated temps while exposed to the atmosphere...therefore the colors are a good indicator of a compromised weld. Thus you want plenty of shielding gas for good coverage (with a gas lens, trailing shield, or even a chamber) and short passes to keep the heat down. You'd like it to come out a bright silver, but typically a light gold color is acceptable (and sometimes beyond that, depending on the application/code). But the less color in Titanium, the less chance it's contaminated.
I know in the tuner world a lot of cats like having those bright, vibrant colors in their high dollar Titanium exhausts...but it's not really a good thing. Honestly, it might now matter on a relatively low stress part, but "now ya know."
Colors in titanium versus stainless