Color is related to Sand. Sand is related to Dirt. Dirt is the opposite of Soap. 
Obstacle is related to Hazard. Hazard is related to Threat. Threat is related to Danger. Danger is related to Careful. 
Color <--RelatedTo--> Sand <--RelatedTo--> Dirt <--Antonym--> Soap 
Obstacle <--RelatedTo--> Hazard <--RelatedTo--> Threat <--RelatedTo--> Danger <--RelatedTo--> Careful 