A colourful closet is wonderful, but there is nothing wrong with having some standard black clothes and accessories. These you can wear on their own, or mix and match with others. Just make sure to invest on some good quality products, which would last long.
A black pair of shoes will get you through formal meetings as well as weddings. Sometimes it happens that you cannot match the colour of your dresses with the shoes, and that is when the black ones will come in handy.
For men and women both, it is better to have 2-3 pairs of shoes (high heels, pumps, sandals etc.) ready for every occasion. Some men prefer to match their belt's colour with their shoes, so in that case, the wardrobe should have some black belts.
The little black dress is not always applicable for women in Bangladesh who rarely wear dresses. Therefore, a black dupatta, scarf or kameez is essential for their wardrobe. A black phulkari, embroidered or benarasi dupatta is versatile and can be worn with any coloured kameez. A black silk scarf will look cute too.
On the other hand, have some tailor made black kameezes for formal and informal events. Also buy some black pants or salwars (palazzos, tapered, whichever shape you prefer) to wear with one-pieces or kurtis. Black crop tops, shirts, sheer blouses, jeans etc. will save you tons of time when you want to don a western look. A black benarasi, chiffon or georgette saree will help you create an elegant look for any special event.
Boys wear many black t-shirts anyway, but a black shirt, blazer or suit is necessary for anyone trying to look more grown up and just plain stylish. A black panjabi for Eid? Anybody would dig that!
Coloured or tinted sunglasses and bags are not quite popular in our country so most of us have these in black in our wardrobes but as mentioned before, instead of piling on lots of things, buy few, good quality, durable ones.
Wearing all black will not give a gothic vibe (unless you are trying to look gothic, which is fine) if you can pull off the right look. Instead of solid black, opt for various shades of grey or white. For example, you could wear a black dress with a white scarf or vice-versa, or, team up a pair of white sneakers with a black shirt.
Grey can become amazing colour if you can add tints of silver, white, blue etc. to it. For women, contrasting a black blouse with any saree also looks good sometimes. If you are worrying about looking the part for a presentation, just go for an all-black outfit.