What about a burnt orange so it doesn't stand out too much from the darker woods but is a splash of color. Don't know how to make it clicky but here's a link at Lowe's
http://www.lowes.com/pd_94101-4-30096ORANGEGLAZE_4294766291+4294791315_4294937087_?productId=3330806&Ns=p_product_prd_lis_ord_nbr|0||p_product_qty_sales_dollar|1&pl=1¤tURL=%2Fpl_OrangesPeaches_4294766291%2B4294791315_4294937087_%3FNs%3Dp_product_prd_lis_ord_nbr%7C0%7C%7Cp_product_qty_sales_dollar%7C1&facetInfo=Oranges/Peaches
or even a lavender if you want something totally off the wall but would still go with the grey and lighten up the bookcases
http://www.lowes.com/pd_93679-4-EB53LAVENDERHEATHER_4294766291+4294791313_4294937087_?productId=3326772&Ns=p_product_prd_lis_ord_nbr|0||p_product_qty_sales_dollar|1&pl=1¤tURL=%2Fpl_PurplesLavenders_4294766291%2B4294791313_4294937087_%3FNs%3Dp_product_prd_lis_ord_nbr%7C0%7C%7Cp_product_qty_sales_dollar%7C1&facetInfo=Purples/Lavenders