As its name suggests, the Spotted Chorus Frog (Pseudacris clarkii) has a pattern of spots of brownish green on a lighter brown/gray background.
In my experience, the intensity of the frog's colors can change. Sometimes the frog is brown with brownish green spots and other times they are light with brighter green spots.
In some individual Spotted Chorus Frogs, the spots are fused together forming a pattern of stripes along the back of the animal, like this individual from Burleson County, Texas.
The Cajun Chorus Frog (P. fouquettei)* is similar in size and shape, but is generally brownish with brown stripes rather than the spotting seen in the Spotted Chorus Frog. However, once again the pattern can vary and sometimes an individual can have partially broken stripes which can give it an almost spotted appearance.
So these two species of frog overlap in areas of east-central Texas and Oklahoma. Their habitat preferences differ slightly with the Spotted Chorus Frog being found in prairies and the Cajun Chorus Frog being found in grassy woodland clearings or ponds but in their range overlap they will often utilize the same habitats. This is particularly true in areas of "anthropogenic prairie" (i.e. man made grassy clearings and pastures). They are both often heard calling from flooded grassy roadside ditches.
Where they overlap, the difference in their calls makes their identification easy. Both species have a dry trilling call like someone scraping their fingernail over the teeth of a plastic comb, but they differ in the speed of in which it is being done.
The Spotted Chorus Frog is a short fast dry trill. The trill itself generally takes around 1/4 of a second and is repeated usually twice a second. The call rate is temperature correlated so in cooler temperatures the call is a bit slower and spaced a bit further apart.
The Cajun Chorus Frog has a much slower trill. It is much more reminiscent of the "fingernail across the comb teeth". The individual call generally takes between half a second and a second and is repeated with less frequently than that of the Spotted Chorus Frog.
* - The Cajun Chorus Frog (Pseudacris fouquettei) has been known by several names of the last 25 years or so. Originally, it was part of the wide ranging Western Chorus Frog (P. triseriata). Later, it was determined that the populations currently grouped under the name Western Chorus Frog actually represented two species. The Texas frogs were now considered to represent the Upland Chorus Frog (P. feriarum). Subsequent research has shown that the populations of Upland Chorus Frog in east Texas, Louisiana and Arkansas represent a separate species, the Cajun Chorus Frog (P. fouquettei).