abstract appearance background bark branches color colored colors colour coloured colours cork cork tree exterior external impervious layers light resistant shadows sky soft stark sunlight sunshine surface textures tree trunk twisted useful Australian bare brown cracked cracks dry edge edges eucalypt eucalypts gray grey lines mottled rough shapes smooth texture textured tree-trunk uneven variations wallpaper white wood black close-up grooves peeling tree trunk botany close closeup crack detail flora floral forest green lumber macro material natural nature old organic pattern structure timber wooden contours gnarled layered patterned patterns shape shaped strips surfaces surfacing cambodian pitted