Not conspicuous, noticeable, or prominent. (Dictionary.com)
Not readily noticeable. (Merriam – Webster)
Not easily or quickly noticed or seen, or not attracting attention. (Cambridge Dictionary)
Someone who is inconspicuous does not attract attention to themselves. (Collins Dictionary)
Not clearly visible or attracting attention. (Oxford Dictionaries)
Inconspicuous. Advanced English.
The Power of Inconspicuous Design.