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.
In modern grammar, modal verbs are a grammatical category of verb. They are a subcategory of the auxiliary verbs. There are nine modal auxiliary verbs in English: CAN, COULD, SHALL, SHOULD, WILL, WOULD, MAY, MIGHT and MUST.
Modal verbs are different from other auxiliary verbs like BE HAVE and DO and also from other verbs in general.
A: Tense:
Firstly, modal verbs always have tense. They are always present tense or past tense:
PRESENT TENSE: can, shall, will, may, must.
PAST TENSE: could, should, would, might.
B: They don't change:
Secondly, modal verbs never change. They always stay the same. They have no third person S in the present tense:
- walks, is, has, does,
cans
They have no plain form (no 'bare infinitive'). And for this reason we don't see them in to-infinitives. A to -infinitive is just the word to followed by the plain form:
- to walk, to be, to have, to do,
to may
They have no -ing form (no present participle):
- walking, being, having, doing,
musting
They have no past participle (no 3rd form):
- walked, been, had, done,
musted
C: Only one modal
Other auxiliary verbs can occur together:
However, we never find two modal auxiliary verbs together:
- *When I finish college, I will can speak English very well (ungrammatical)
- When I finish college, I will be able to speak English very well.
D: Always the first verb:
A modal verb is always the first verb in the verb phrase:
- *She ____ have been studying might English. (ungrammatical)
- She might have been studying English.
More information
Modal verbs often tell us about modality. This means they tell us about possibilities and necessities, or rules and obligations. However, other verbs and other types of word also have meanings relating to modality. The important fact about modal verbs is that they have a certain grammar. They are a grammatical type of word.
Some verbs sometimes have a similar grammar to modal verbs. For example the verbs OUGHT, DARE and NEED. Some people call these semi-modals.
Best Answer
There is a fixed list of modal verbs and semimodals.
Modal verbs: can, could, may, might, shall, should, will, would, and must.
Semimodals: ought + to-infinitive, have + to-infinitive, be able + to-infinitive, dare and need, had better (that is mostly classified as a compound verb), used + to-infinitive or used to + do-insertion.
While "have (got) to" isn't a modal verb, "have" is an auxiliary verb along with "be" and "do".
"Have to" or "have got to" (British English) also carries a meaning of something obligatory in the same way modal verbs do:
The way grammar says it:
"Have" is an auxiliary verb. Modal verbs are followed by infinitives without "to". In "have to", "have" is the main verb that follows a to-infinitive.
In the Simple Past and Simple Present it doesn't follow an auxiliary verb.
In the Future Simple it is preceded with an auxiliary verb "will".
In the negative sentences it always follows an auxiliary verb.
In the interrogative sentences an auxiliary verb comes first and is followed by a subject, which is followed by "have to".
However, it is accepted by some dictionaries and sources to define "have to" as a modal verb. (Oxford Learners Dictionary, Perfect English Grammar, Ginger, LinguaPress, ThoughtCo, Woodward English)