Technically, the tense should match, so since we're using the perfect tense (conditional perfect in fact), you should use was.
But both could have ... is and could have ... was are acceptable in this case.
Why? Well, it's because your clause about the paprika being similar to the bell pepper might be true for a long time, and might continue to be true even in the present, so it might be okay to use is.
Maybe not. Maybe the paprika is rotten by now, or already eaten. Then is would make no sense. But a situation continuing to the present would justify use of the present tense is.
Consider:
"I could have gone shopping, because the supermarket was near."
"I could have gone shopping, because the supermarket is near."
If the supermarket has not suddenly moved, it probably still is near – it is now, and it was then – so either one is acceptable.
But some things do not last so long:
Correct: "I could have stayed longer, because it was early in the morning."
Incorrect: "I could have stayed longer, because it is early in the morning."
Unless you are describing something in the very recent past (minutes or hours ago), the fact that it is now early probably has nothing to do with the situation in the first half of that sentence, so mixing the past and present tense in this last example doesn't really work.
Present Perfect implies a strong connection to the present (time of speaking). Often, the connection is no more than that the past action being referred to happened very recently.
1: The plane crashed there last year
2: ??The plane has crashed there last year (an extremely unlikely utterance)
3: The plane crashed there just now
4: The plane has crashed there just now
Simple Past doesn't necessarily imply an action occurred further back in the past than something described using Present Perfect - it's just a more "general-purpose" verb form. Thus #3 and #4 are both normal English.
Best Answer
It is also past tense.It talks about the recent past.
The above sentence is in the past.If we use Just, it does not mean that it is present.It refers to recent past.
It is called the present perfect which talks about the recent past but completed action.
I have passed my M.A exam
It is also called present perfect but the action might have happened long ago.
Now I made it is a song.In songs we can not search for grammatical correctness.
It is also past tense though it refers to present time.
In English there is no one to one correspondence between time and tense.