The Blue Wool Scale (BWS) indicates the lightfastness of colourants. Lightfastness is the chemical stability of a pigment or dye under long exposure to light.
A rating of between 0 and 8 is awarded. 0 denotes extremely poor lightfastness, whilst 8 denotes excellent lightfastness.
Each Colourmount board has its individual BWS rating marked on the reverse. A list of the BWS ratings for each Colourmount board is shown below:
| Name | Ref No. | BWS Rating |
| Almond | 1004 / 3004 | 3 |
| Antique White | 975 / 3975 | 5 |
| Aqua | 3993 | 5+ |
| Arctic White | 889 / 389 | 5 |
| Bamboo | 1007 / 3007 | 5 |
| Barley | 989 / 3989 | 5 |
| Beaujolais | 849 / 349 | 4 |
| Beige | 810 / 310 | 3 |
| Black | 872 / 372 | 4 |
| Blossom | 805 / 305 | 3 |
| Bluebell | 840 / 340 | 4 |
| Bottle Green | 832 / 332 | 4 |
| Bronze | CM18 | 5+ |
| Buff | 803 / 303 | 3 |
| Burgundy | 853 / 353 | 4 |
| Buttermilk | 1003 / 3003 | 4 |
| Cameo | 984 / 3984 | 3 |
| Chalk White | 1001 / 3001 | 4 |
| Champagne | 807 / 307 | 4 |
| Charcoal | 825 / 325 | 4 |
| Chestnut | 720 / 3720 | 3 |
| China Red | 1040 / 3040 | 4 |
| Chive | 931 / 3931 | 4 |
| Chocolate | 813 / 313 | 4 |
| Clear Water | 951 / 3951 | 5 |
| Cloud | 845 / 345 | 5 |
| Cobalt Blue | 842 / 342 | 4 |
| Coffee | 811 / 311 | 3 |
| Copper | CM17 | 4 |
| Cinder Grey | 3998 | 4 |
| Cream | 802 / 302 | 4 |
| Cream Ingres | 986 / 3986 | 4 |
| Dawn Mist | 877 / 377 | 4 |
| Dove Grey | 822 / 322 | 3 |
| Dusty Pink | 855 / 355 | 4 |
| Ebony | 3999 | 4 |
| Eggshell | 701 / 3701 | 3 |
| Emerald | 3991 | 4 |
| Essence White | 917 / 3917 | 4 |
| Falcon | 507 / 3507 | 3 |
| Forest Green | 1031 / 3031 | 4 |
| Geranium | 3997 | 4 |
| Gold | 862 / 362 | 5 |
| Granite | 828 / 328 | 4 |
| Grape | 890 / 390 | 4 |
| Green Gold | CM13 | 5+ |
| Harvest Beige | 920 / 3920 | 2 |
| Haystack | 965 / 3965 | 3-4 |
| Hazelnut | 859 / 359 | 4 |
| Holly Green | 833 / 333 | 4 |
| Honeysuckle | 982 / 3982 | 4 |
| Iced Crystal | 885 / 385 | 3 |
| Iced White | 973 / 3973 | 4 |
| Ivory | 801 / 301 | 4 |
| Laurel | 835 / 335 | 4 |
| Leaf Green | 1030 / 3030 | 4 |
| Lemon | 3995 | 5 |
| Lime | 3992 | 5 |
| Loganberry | 715 / 3715 | 4 |
| Lupin | 846 / 346 | 4 |
| Maple | 834 / 334 | 3 |
| Midnight | 839 / 339 | 4 |
| Moorland Green | 831 / 331 | 4 |
| Mushroom | 1023 / 3023 | 4 |
| Nightshade | 954 / 3954 | 4 |
| Off White | 981 / 3981 | 4 |
| Old Gold | 864 / 364 | 5 |
| Old Ivory | 809 / 309 | 3 |
| Or | 506 / 3506 | 3 |
| Osprey | 725 / 3725 | 3 |
| Oxford Blue | 843 / 343 | 4 |
| Oyster | 808 / 308 | 4 |
| Pale Gold | CM14 | 5+ |
| Pale Silver | CM12 | 5+ |
| Pastel Blue | 844 / 344 | 4 |
| Pastel Green | 829 / 329 | 4 |
| Pastel Pink | 856 / 356 | 4 |
| Pearl | 800 / 300 | 4 |
| Pigeon | 945 / 3945 | 3 |
| Platinum | CM19 | 4-5 |
| Polar White | 1002 / 3002 | 4 |
| Poppy | 851 / 351 | 4 |
| Porcelain | 847 / 347 | 4 |
| Portland | 821 / 821 | 5 |
| Putty | 983 / 3983 | 4 |
| Rose Gold | CM16 | 5+ |
| Rouge | 850 / 350 | 4 |
| Sage Green | 830 / 330 | 3 |
| Sand | 804 / 304 | 4 |
| Sand Ingres | 985 / 3985 | 4 |
| Sandstone | 925 / 3925 | 4 |
| School Grey | 826 / 326 | 4 |
| Seal Brown | 815 / 315 | 4 |
| Sepia | 814 / 314 | 3 |
| Shamrock | 3990 | 4 |
| Silver | 861 / 361 | 5 |
| Silver Birch | 710 / 3710 | 3 |
| Simply White | 891 / 391 | 3-4 |
| Sky | 3994 | 5 |
| Slate | 841 / 341 | 4 |
| Smoke Grey | 824 / 324 | 5 |
| Snow White | 971 / 3971 | 3 |
| Soft White | 875 / 375 | 5 |
| Solar Gold | CM15 | 5+ |
| Spice Brown | 916 / 3916 | 4 |
| Stone | 823 / 323 | 4 |
| Sugared Almond | 882 / 382 | 3 |
| Tangerine | 3996 | 4 |
| Unicorn | 501 / 3501 | 3 |
| Vanilla | 1015 / 3015 | 4 |
| Warm Ivory | 806 / 306 | 4 |
| White | 871 / 371 | 3 |
| White Gold | CM11 | 5 |
| White Ingres | 987 / 3987 | 4 |