Why was there a Jewish Zionist group named the Jewish Colonial Trust Why was colonial used ?

Simply because Zionism is a colonial movement.
Zionist pioneers and leaders labeled their Zionist projects as colonial projects. The social and economic institutions founded by the early Zionists, which were central to the success of the Zionist project, were also unquestioningly understood by all and described as colonial. The most important of these institutions was the Jewish Colonization Association (in 1924 renamed the Palestine Jewish Colonization Association , and was renamed again and now known as the Jewish Charitable Association (ICA))This body was originally established by the German Jewish philanthropist Baron Maurice de Hirsch and later combined with a similar organization founded by the British peer and financier Lord Edmond de Rothschild. The JCA provided the massive financial support that made possible extensive land purchases “and the subsidies that enabled most of the early Zionist colonies in Palestine to survive and thrive before and during the Mandate period. Unremarkably, once colonialism took on a bad odor in the post–World War II era of decolonization, the colonial origins and practice of Zionism and Israel were whitewashed and conveniently forgotten in Israel and the West. In fact, Zionism—for two decades the coddled step-child of British colonialism—rebranded itself as an anticolonial movement.
The colonization plan was prior to the 1900s. An article about a Conference of Zionists published on July 20, 1899 in the New York Times depicts how the Conference sought to “colonize Palestine” and discussed the purchasing of land with English Zionists.
The article explains that the conference discussed a paper from the English Zionist Federation “proposing the reestablishment of Judea as an independent State, suggesting the purchase of the Maccabean sites in Palestine, and the beginning of the work by the establishment of a Jewish colony and a Jewish Agricultural College there.” It further clarifies that “The site to be purchased comprises about fifty acres, six miles from a station on the railroad between Jappa and Jerusalem, and within sight of the sea and a large stretch of the Palestinian coast.” It notes that English Zionists have gathered 2,500 dollars in the currency of the period and request that quantity from the American Zionists. The article also explains that “On motion of Dr. Wise, the Federation voted $100 as the nucleus of the required fund of $2,500, the remainder to be raised by subscriptions from the 125 societies and individuals, both Jews and Gentiles. A general appeal to the public will be made.” It also conveys that delegates will be elected at the Zionist meeting in Baltimore.
The straightforward and comfortable manner with which the colonization is pursued is indicative how, before having to be concerned with the image of Zionism and public relations, Zionist leaders depicted their movement as a colonial mission during a time in which European nations were colonial powers.
When Palestinians understood the motives and the plan of the Zionists to build a state on their homeland, they rejected such preposterous colonial notion. Palestinians refused to sell their lands , and are still doing so until the current day. The Zionists then realized for their colonial project to work , they need to ethnically cleanse the Palestinians, as of what happened in the Nakba/catastrophe in 48, The Naksa in 67, and until this very day.
Mussolini’s Zionist fascist friend Jabotinsky made it clear :

Zionist colonization must either be terminated or carried out against the wishes of the native population. This colonization can, therefore, be continued and make progress only under the protection of a power independent of the native population – an iron wall, which will be in a position to resist the pressure to the native population. This is, in toto, our policy towards the Arabs…” (Vladimir Jabotinsky, The Iron Wall, 1923).

Jabotinsky was a Russian Jewish Revisionist Zionist leader who founded well renowned Zionist terrorist organizations like Irgun in Palestine.
The Zionists’ colonial enterprise, aimed at taking over the country, necessarily had to produce resistance.
Jabotinsky wrote in 1925:

“If you wish to colonize a land in which people are already living, you must find a garrison for the land, or find a benefactor who will provide a garrison on your behalf.… Zionism is a colonizing venture and, therefore, it stands or falls on the question of armed forces.”(Expulsion of the Palestinians, P. 45)

At least initially, only the armed forces provided by Britain could overcome the natural resistance of those Palestinian Arabs being colonized.
Zionist leaders consciously recognised that state anti-Semitism was essential to their colonial project, writes Massad.
Rima Najjar