Here are some tips to use when choosing your colors to draw a tomato.
Drawing red objects such as a shiny tomato can be difficult. You need to get your reds dark enough and the shadow areas very dark but there still needs to be a very subtle transition from the dark tones to the main mid tone color of red. You want to convince the viewer that your tomato is a very round red tomato and that the shadows are still red but very dark. Practicing a color tone bar is a good idea before drawing the tomato. I suggest you start with a tone bar of mid red close to the color of your tomato. Then create the darker tones using a deep red wine color such as #194 red violet. Add the red and orange colors as your tone bar gets lighter. Use hardly any sepia at first.