This can be done easily in Illustrator.
OPTION 1 (top JPG as example, and top image on the second JPG):
1) You need to duplicate the text you want to apply the effect on.
Type your text and then use the "transform" command in the menu "object", then select "move". In the window of "move", put zeros everywhere to duplicate this text in the same same position. Press "Copy"
2) Select the text on the front. Add a big stroke of a different color with round corner and the edges aligned to center (see on pictures).
3) Select that text and do a "create outline" (in the menu type/create outline)
4) Select again this top text. Then go in the menu "object" and select "expand", check all the boxes. This will separate the border from the inside of the text.
5) Erase the outside border from the graphic, for each letter and keep the inside part only. You can use the white arrow for from the selection tool and simply click a corner of your letter, and press delete twice. Or you can ungrounp this and simply select the entire part, and delete it.
6) Fill that inside part with the tone you want, a light bright yellow to imitate your example. And fill the text still untouched in the background with a darker yellow with more magenta in it.
7) If you want to smooth a bit the effect, you can add a small border on the inside part; on my example I used a yellow that is between the 2 yellow for the color recipe. It gives some smoothing effect and blends a bit the 2 colors together. My border is 3pts thick.
But you could probably use the blend tool as well, it's just tricky something on curvy letters.
You can change the values to fit you preferences and the font you'll use for this. At this point you can play with the strokes to change the thickness of the inline. This is just an example.
OPTION 2 (see second JPG, example on bottom):
1) Simply choose a very thin font, and duplicate a copy behind it.
2) Fill the duplicated set with a thick stroke from the outside, and adjust.
This option may look better with think fonts or script style.