You've given us a bit of a challenge there! I would recommend starting with climbers suitable for a north wall:
Hydrangea anomala subsp. petiolaris, Garrya elliptica - esp. 'James Roof' and various species of Parthenocissus. Variegated ivy would provide some nice pale colours, but in shade it tends to be less variegated!
You'll need some woody plants to provide some depth and height. Try variegated holly and Euonymus fortunei cultivars, Chaenomeles x superba, Cotoneaster species, Jasminum nudiflorum and Mahonia aquifolium cultivars.
At the base of all those you can plant some herbaceous perennials. The following will tolerate dry shade. You haven't said the border is either of those things but given that it's next to a three metre wall I'm assuming it's both. So try these:
Epimedium species, Heuchera cultivars, variegated vincas (vinca can be invasive, picking a variegated one makes this less likely), Brunnera macrophylla.
You can go to town on some of the spring bulbs - snowdrops, wood anemones and white siberian squill would suit you.
Polystichum and Dryopteris ferns usually cope well with dry shade. Keep them well-watered when you first plant them.
In the summer you can use bedding plants that don't mind shade - begonias and bizzie lizzies will take it.
None of my recommendations takes into account your soil type so do a soil test and check before buying that each of these is suitable for your soil.
I agree that pastel and white plants will help the area look brighter, but if you stick to those you'll have no structure, so pick them where you can - i.e. in bedding, bulbs and variegated plants.
Good luck, it sounds like a fun project to work on. Let us know how you get on.