Paint shops abound in Singapore. Most industrial estates will have at least one. Painting from around $200/room up.
Be sure you get permission from the landlord to paint using "special" colours. Also you might be able to get the landlord to do the outside if it is really in need of it. Again, it's best to check before a major colour change otherwise, you might find you have to pay two times, in order to restore the property
back to it's original condition (they will use it as a means to keep your deposit).