I Found A Black Snake With Orange, Yellow And White On Its Back, Was It Venomous ?

Without any further information or description of the snake, it is difficult to tell you exactly what type of snake it was. The closest snakes that fit your primary description are either the coral snake or the milk snake, however the main colour of this snake is thought to be red.

Some milk snakes have a striking resemblance to coral snakes, and there can often be some confusion between the two. You may have heard that a common mnemonic can be used to distinguish between those snakes similarly coloured to the milk snake that are venomous and those that are harmless. There are many variations of this mnemonic but one version is ‘red on yellow will kill a fellow, but red on black is a red of Jack’. This relates to the pattern of colours on the back of the coral or milk snake.

There are several snakes that are commonly found in Texas so if you come across snakes on several occasions that it might be worth becoming familiar with what venomous ones look like so that you can steer clear of them and teach your children to do the same if they come across one.

The only way that you are going to know for sure what type of snake that you saw and whether or not it is venomous is to take a picture of it to an expert. They will probably be able to identify it for you on the spot and give you all the information that you will need. Ask them if there are any venomous snakes that are commonly found in your area and if they could give you a guide explaining any distinguishing marks that you can look out for. Going to an expert is your best chance of identifying the snake you found.

Head shape is only indicative of pit vipers (rattlers, copperheads, moccasins) and is not an accurate way to identify venomous snakes, since non-vipers can also be venomous.  So please do not rely on this.
 
To be certain, you will need to either take a picture or good description of the snake to an expert, because without a picture where we may identify it, we cannot accurately say the danger.  Describe the snake to a herpetologist or expert at the university nearby.  Or, alternatively there are also many website with pictures you may use to help identify the animal and discover its potential for harm. 
 
Here is one such site that may be helpful to you.
www.backyardnature.net

A milk snake is black with orange, yellowish-white rings and is not poisonous. Note the red and black touch and not the red and yellow rings. However a Coral snake is similar in color and pattern with the exception that the red and yellow touch in the pattern. The Coral snake is a very poisonous snake. Ever hear the saying "red and yellow kill a fellow, red and black venom lack?"

Probably, usually snakes with bright colors are dangerous ( unless it is a mock snake)

It's probably a mud snake. .