Usage change

{| class="wikitable"
|-
{{party colour|party name}}
| Candidate
|
|-
...
|}

or to override the default width of 10px,

{| class="wikitable"
|-
{{party colour|party name|1px}}
| Candidate
|
|-
...
|}

or to override the default rowspan of 1,

{| class="wikitable"
|-
{{party colour|party name|rowspan=3}}
| Candidate
|
|-
...
|}