abstract appearance background bark color colored colors colour coloured colours cork cork tree exterior external impervious layers light resistant shadows soft sunlight sunshine surface textures tree trunk useful branches sky stark twisted cut cutout isolated piece trees wood wooden maple plant forest nature oak oaks plantation Quercus suber red Sardinia undergrowth woodland grove Quercus shade stone suber wall texture wallpaper rough crop Expose harvest strip cortex down moss pattern pine cork oak crack crevasse crevice rugged