good question, TheBanffie.
https://greens.scot/Code-of-Conduct
You could get in touch and make a complaint to the SGP.
If a party has discriminated, the EHRC has this advice:
'Political party
A complaint to the Chair (or equivalent) of the political party may be made if electoral conduct is:
• factually incorrect
• damaging to good relations
• makes a false statement about the character and conduct of a candidate
• incites hatred for persons with a protected characteristic
• breaches the Party’s own code of conduct.
Local authority
Any complaints about the behaviour of existing elected members can be referred to the local authority’s monitoring officer, who is responsible for the complaint if there is an allegation that a member has breached the local Code of Conduct.
Police
Electoral conduct which is likely to stir up racial or religious hatred or hatred because of sexual orientation should be reported in England and Wales to the Chief Constable or other senior police officer and in Scotland to the police. The test for incitement offences is set high, so before making a complaint it is a good idea to consult local community groups and councillors to see if there is a consensus on whether the conduct is likely to incite hatred or lead to other offences. Even if material does not meet the criminal threshold for incitement offences, the police may still decide to discuss the complaint with the perpetrator.'
https://www.equalityhumanrights.com/sites/default/files/equality-and-human-rights-law-during-an-election-period.pdf