There are a couple of points to be mindful about
- As Mark rightly pointed out, red is often are often used as as an visual aid to indicate failure . Often red is also used to highlight danger or error states which could cause confusion with regards to what is being indicated here.It is also a strong accent color which is used to drive a strong call to action To quote this article from color wheel
Red is the color of fire and blood, so it is associated with energy,
war, danger, strength, power, determination as well as passion,
desire, and love.
Red is a very emotionally intense color. It enhances human metabolism,
increases respiration rate, and raises blood pressure. It has very
high visibility, which is why stop signs, stoplights, and fire
equipment are usually painted red. In heraldry, red is used to
indicate courage. It is a color found in many national flags.
Red brings text and images to the foreground. Use it as an accent
color to stimulate people to make quick decisions; it is a perfect
color for 'Buy Now' or 'Click Here' buttons on Internet banners and
websites Red brings text and images to the foreground. Use it as an
accent color to stimulate people to make quick decisions;
- I strongly recommend against using colors only to highlight states since it violates accessibility guidelines as a colorblind person would not be able to see the difference. To quote the WCAG guidelines
1.4.1 Use of Color: Color is not used as the only visual means of conveying information, indicating an action, prompting a response, or
distinguishing a visual element. (Level A)
Since you are denoting incoming and outgoing calls, a design you could potentially reuse is how phones handle the history for incoming and out going calls. To show how Android does it
Here is how iOS does it
In both cases the applications use a combination of colors and opposing icons. I would suggesting using a similar metaphor along with opposing icons and text to highlight which were the outgoing and incoming calls.