unsupported operand type(s) for -: 'list' and 'list'

```python
deltaE([(1, 2, 3), (4, 5, 6)], [(7, 8, 9), (11, 12, 13)], input_space="CAM02-UCS", uniform_space="CAM02-UCS")
```

gives:

```
TypeError: unsupported operand type(s) for -: 'list' and 'list'
```