Adding text in Photoshop

[cristphoto1]

I have the latest Photoshop version on my Windows computer.  I want to add text to an existing photo.  I made the canvas 20x30 as that's the print size I want.  I made the image about 15x24 so it appears to be on a mat.  I want to add text to the "white mat" area and when I do the text is a very light yellow even though I selected black as the text color.  How do I make the text black?  Or can't you print on an area thats not the actual image?  I'm a rookie at adding text to images so thanks for any help. 

[S_Gans]

You can definitely add text on your layer - and it should create a NEW layer, with just the text on it. Note that it would only show if your canvas size is sufficiently large, outside the image (in other words, it won't work outside existing canvas size).
If that's all good - if you're creating your text on actual canvas, then the yellow may be a result of layer blending modes. Find your text layer - and look at the top of the Layer Panel. You should see a setting that says Normal, and 100% opacity. If it says anything else, try changing that setting.