Could be grease from an axle or wheels bearing. Inspection is needed to be sure.Use this link to find a good shop near you.
https://repairpal.com/repair-shops
Alex
RepairPal Certified shops can diagnose and repair your 2007 Lexus RX350. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.
Don’t worry - it’ll wash off!