1) Blackish 2) Tending toward black 
turning black
• (a.) Growing black; changing to a black color; approaching to blackness. • (a.) Growing black; changing to a black color; approaching to blackness.
blackish
blackish
Ni·gres'cent adjective [ Latin nigrescens , present participle of nigrescere to grow black, from niger black. See Negro .] Growing black; changing to a black color; approaching to blackness. Johnson. 
turning black
nigrescent Other related 'dark; shadow, shade; black' units: lygo-; melan-; nocti-; nycti-; scoto-; skio-; umbra-.
tending toward black; blackish.