created toolchain ends up with an additional channel color
When I create a toolchain: [1.json](/uploads/bcc74bd465e922514b0550e245cad72f/1.json), it ends up with an extra channel color:
```
"channel_colors": {
"": "#000000",
"test": "#005500",
"train": "#aa0000"
},
```
which makes the toolchain invalid.
[prefix.tar.xz](/uploads/51757b07d4efcbcf3e332de6b902dcc2/prefix.tar.xz)
issue